"The Romance of the First Air Adventurers" (continued 2)

“We shall have Pierre over here this evening,” Gaston chuckled. “That’s the signal that I want him.”

Sure enough, soon after dark, Pierre appeared. A few words explained the situation. He was off duty now for the night and free to do as he pleased.

“Leave it to me,” he said. “I will be back in an hour.”

He returned with a rough plan of the section of the prison in which Yvette was confined. Her cell occupied a corner on the first floor at the head of a flight of steps leading down to the big courtyard. If Yvette could get out of her cell it would be an easy matter to reach the door leading to the yard. But to get over the high wall, quite unclimbable, was a difficult problem. The entrance from the roadway was always guarded by two warders who occupied little separate lodges placed one each side the gateway.

“I can get her out of her cell,” said Pierre, “but how to get her out of the yard I don’t know. I can get a false key to her during the day, but if I were found in that quarter of the prison at night it would mean instant dismissal. On that point the rules are inflexible and we cannot risk it.”

“No,” said Gaston, “it is absolutely essential that you shall remain in the prison. But I think I can see a way.”

He crossed the room to an old-fashioned bureau and produced from a drawer what looked like a heavy short-barrelled pistol.

“Gas!” he said laconically, “fire that at a man’s face within five yards and he will drop like a log. It holds four shots and makes no noise. If Mademoiselle can get this she can knock out the two men at the lodge and easily slip out. You can bring her straight here, and we can hide her until she can get away.”

“She cannot hide that in her cell,” said Pierre, “but I can hide it in the courtyard. Write her a letter telling her exactly what to do and where the pistol will be. I can slip into her cell a skeleton key which will open the door and also the door at the bottom of the steps. But you must manage the rest; I cannot do any more. She must get out immediately after the last visit of the warders at nine o’clock.”

“Thanks very much, Pierre,” said Jules. “I can see no other way, and at all costs we must try to get her out. Neither my sister nor myself will ever forget.”

Speedily a letter was written which gave Yvette full details of what was proposed, and Pierre was about to leave when Jules asked him if he had heard anything of the secret aeroplane.

Pierre shook his head.

“There are a lot of privately owned aeroplanes about here,” he said, “but I don’t know anything more than that. I have seen the one you refer to going up at night—the house is in plain view from my room on the first floor of the prison—but I never heard there was any secret about it, and there are so many aeroplanes about that no one takes any notice of them.”

Jules told him all they had found out, and of their suspicions, and found Pierre was able to give them valuable information.

The aeroplane shed, he told them, was just where Yvette had located it. Above it—and this was important—were some rooms which were used, apparently, as offices.

“I have often,” said Pierre, “seen a man come from the offices with what looked like plans, make examination and measurements of the machine, and then go back. But I never took much notice; I had no reason to.”

Pierre left, taking with him the letter to Yvette. For an hour Jules and Gaston discussed the situation.

“We must get her out to-morrow,” declared Gaston, “or else they may take her away and we shall not be able to find out where she is. Manton ought to fly over to-morrow night. If we can get Mademoiselle Pasquet out she can hide here quite safely for a few hours, but there will be a very close search when her escape is discovered.”

“I’ll get the message to Manton at once,” said Jules.

And so it happened that Dick and Le Couteur, who had been waiting for hours in a state of tense anxiety, received a few minutes later the call.

“M M M begins To-morrow night stop Come early as possible stop Three lights in triangle safe stop Four keep off M M M ends.”

“At last,” said Dick grimly, with a look on his face that boded ill for some one. He looked drawn and haggard, and even Le Couteur could hardly repress a shudder at the savage determination that blazed in his eyes.

For Yvette the next day was one of misery. Time after time she was dragged from her cell and taken before the Governor of the prison, and Kranzler, to be pitilessly cross-questioned and even threatened with violence. But even though she knew well that the two brutes were quite capable of carrying out their threats nothing could break the spirit of the French girl. To all their questions and menaces she turned a deaf ear and nothing they could say would induce her to affirm or deny anything. Utterly worn out she was at length roughly bundled back into her cell, where she dropped exhausted on the miserable apology for a bed. At least she was alone.

It was about five o’clock and she had fallen into an uneasy doze, when she was awakened by a slight noise at the door. She saw the observation grille slide back and, pushed through the grating, a tiny parcel fell with a subdued clink on the floor. Then the grating was closed.

Hastily she sprang to her feet and seized the parcel, a new hope surging in her breast. It could only mean help!

Inside the parcel was a letter, unsigned of course, but in Jules’ handwriting, and a small key.

Nine o’clock came, and with all the wearisome ceremony dear to the German heart, the guard, accompanied by a wardress, made its final inspection for the night. A few minutes after the big prison was as silent as the grave.

Half an hour later Yvette cautiously fitted the key into the lock. It had been well oiled, and the door swung open without a sound. Creeping down the flight of steps Yvette found that the key also opened the door at the bottom, and in a moment she was in the yard.

Rain was falling heavily. There was not a ray of light in the yard excepting a faint gleam which showed the position of the warders’ lodges.

Before leaving her cell Yvette had pulled her stockings over her boots, and moving without a sound she groped her way along the wall. A few feet from the door she found the big stackpipe which brought the rain water from the roof. Stooping she lifted the iron grid of the drain and thrust in her hand. Her fingers closed on the butt end of the gas pistol.

Silently, following along the wall in preference to crossing the courtyard, she stole towards the lodge. Complete surprise was essential.

With the pistol ready in her hand, she softly opened the door of the lodge on the right of the gateway. Luck was with her again. The two men, in defiance of rules, were in the same lodge talking quietly.

The noise of the door opening brought them to their feet with a jump. But they were too late. Only ten feet away from them Yvette pulled the trigger twice in rapid succession. There was no more noise than a slight hiss as the gas escaped and the two men dropped insensible. Snatching up a bunch of keys from the table, Yvette herself half-stifled, quickly got outside and closed the door. A moment later she had opened the wicket-gate and slipped through. She almost fell into the arms of Jules and Gaston, and at top speed the three raced through the rain for Gaston’s farm.

Luckily, the pouring rain swiftly obliterated their footprints, but they had hardly got into hiding, wet through but triumphant, when pandemonium broke out in the prison, and the frantic ringing of the big bell announced the escape of a prisoner. The two warders, of course, had speedily recovered, and hastened to tell their story, and a quick search had revealed that Yvette’s cell was empty. A few minutes later search parties were hurrying in every direction in pursuit of the fugitive.

Gaston’s farm, lying close to the prison, was naturally one of the first places to be visited. Gaston, smoking peacefully by the fireside, soon heard, as he expected, the savage clamour of dogs in the farmyard mingled with agonised cries for help.

He hurried out. Two warders, one of them badly bitten, were backed against the fence, hardly keeping at bay with their sticks a couple of powerful dogs.

Gaston called off the dogs and, full of apparent solicitude, expressed his regret. He listened to the guards’ explanation.

“She cannot have been here,” he declared, “the dogs would have bitten her to pieces. But, of course, we will look round if you like.”

The guards, however, were more than satisfied. Gaston’s argument was backed by their own experience, and they were quite ready to be convinced if they could only get away from the ferocious dogs who continually prowled about snarling as though even the presence of their master was hardly sufficient to protect his visitors. They little dreamed that the savage brutes would indeed have torn Yvette to pieces had not Gaston thoughtfully taken the precaution to lock them up before he and Jules started to rescue her!

Away at Verdun Dick stood beside the Mohawk waiting impatiently in the dark. Time and again he had tested every nut and screw in the machine; time and again he had run the powerful engine to make sure that it was in working order.

At last the longed for moment for action came. Anything was better than long drawn-out suspense.

He wrung Le Couteur’s hand as he stepped into the machine.

“I’ll be back with her by dawn,” he said, “or else—” there was no need to finish the sentence.

He had not gone five minutes before Le Couteur received a message from Jules announcing that Yvette had escaped. If only Dick had known!

It was raining hard when the Mohawk rose into the air, but Dick was beyond caring for the weather, and anxious only for Yvette, he sent the helicopter tearing through the darkness eastward to Berlin. He drove almost automatically, his thoughts intent on the girl ahead of him.

As he approached Berlin, the weather cleared and the rain stopped. All around him were the navigation lights of the German mail and passenger planes, hurrying to every quarter of the Empire, and, even in his anxiety, Dick was conscious of an uneasy feeling of irritation at the thought that England was being left so far behind in the race for the mastery of the air.

Then he caught sight of the great beams of light that marked the position of the huge Berlin aerodrome, and a few minutes’ flying brought him above Spandau. He circled twice, looking for Gaston’s signals, and at last he dropped lower, caught the gleam of the three lanterns which Gaston had placed to guide him, and brought the machine swiftly down beside the big barn. Then he leaped from his seat.

He nearly gave a shout of joy that would have aroused every German within a mile! For there, in the light of the lanterns, stood Yvette herself.

There was no time for explanation.

“Now’s your chance,” gasped Jules, wild with excitement, “the German plane has just gone up!”

Dick’s face hardened instantly.

“Get in, Yvette,” he said curtly.

Yvette stared in utter astonishment. This was a new Dick with a vengeance! All his usual graceful courtesy had dropped from him in the instant; the sheer fighting spirit was on top and Dick was, for the moment, the officer giving commands to his subordinates. His face was set like granite, and into the keen eyes there came a look Yvette had never seen there before. The cheerful, laughing “pal” had gone; in its place stood the fighting machine, pitiless and efficient.

For an instant the girl was almost on the edge of rebellion; then she turned, and, without a word, took her place in the machine. As she did so, she caught Dick’s eye. For an instant the stern face relaxed; then the iron mask shut down again.

For five minutes, while Yvette put on her leather helmet, Dick studied the plan which Jules showed to him by the light of a shaded lantern. When the Mohawk jumped into the air every detail of it was photographed indelibly on his brain.

For three thousand feet the Mohawk shot upward at a speed which left Yvette dizzy and breathless. Then they hung motionless, as Dick peered anxiously earthward. Were they high enough?

With a smothered exclamation Yvette pointed downward. Far below them a light was circling swiftly, darting hither and thither like a will o’ the wisp. No mail plane would behave like that. Dick decided that here was his quarry.

Silently the Mohawk came down till it was not more than five hundred feet above its unsuspecting prey, the loud drone of whose engine came clearly on the air. Dick swung round in a circle, following every movement of the machine below, with a swift precision which Yvette keenly appreciated.

Dick had made up his mind that the offices above the aeroplane shed probably held the key to the problem they had to solve. He knew he could destroy the machine itself. But that would not be enough if the plans remained intact; a new machine could quickly be built. If he could destroy the plans, on the other hand, there would be at least a lot of delay, which would enable the French agents to perfect their plans for discovering the secret. In all probability, he reasoned, the office would serve as the draughtsmen’s workroom, and if this were so, a well-placed bomb might destroy the labour of months.

So he watched and waited, until at length they saw the German aeroplane going home. It came down in a wonderfully steep descent which was enough to tell Dick that the Germans had indeed made a discovery of great importance, and landed so slowly that Dick could hardly believe his eyes. But, at least, he saw enough to be sure that the descent was not the vertical drop of his own helicopter. His secret remained his own!

Close beside the shed a couple of hooded airmen alighted. Lights were switched on and they began a careful examination of the machine. Five hundred feet above Dick watched the figures with interest.

Suddenly the men below stiffened and looked skyward, listening intently. Evidently they had caught the faint sound of Dick’s propellers.

A glance through his bomb sights showed Dick that he was in the position he desired. There was now no possible escape for the craft below.

Then one of the men pointed upward. Even in the darkness he had caught a glimpse of the Mohawk.

Dick’s hand shot to the bomb controls and he pulled a trigger. A petrol bomb fell squarely on the German plane and burst with a soft explosion, barely audible.

A sheet of fire followed, and in an instant the German plane was a mass of flames, fed by the petrol which streamed from its tanks. One of the Germans was caught in the outburst and apparently died almost instantly.

The second man, however, dashed into the office. The Mohawk moved forward a few feet and three more bombs fell in quick succession, right on the roof of the shed. Then, her work done, she rose high into the air and Dick and Yvette watched the results.

The shed below them was already a furnace. Apparently there must have been some petrol tanks there, for no ordinary building could have burned so furiously. In a few minutes nothing remained but a heap of glowing embers.

Dick watched keenly for the man who had run into the office, but he never reappeared, and it was evident that, trapped by the flames, he had been unable to get out in time, and had perished. Dick little suspected at the time how important the fate of that man was to prove.

Then Dick set the Mohawk at top speed for home. Just as dawn was breaking Verdun loomed ahead. Yvette was saved.

Two days later the Berliner Tageblatt told how the famous scientist, Professor Zingler, had perished in a fire which had destroyed his laboratory at Spandau. The fire was attributed to an explosion of petrol on the professor’s aeroplane which had set light to the office. Unfortunately, the paper added, all the professor’s valuable papers and books had been lost.

The secret of the Zingler aeroplane had perished, and the seven dots were never heard again.

Chapter Four.

The Sorcerer of Soho.

“Unless we can solve this terrible mystery in the course of a few weeks, it is hardly too much to say that England is doomed.”

The speaker was the white-haired Professor Durward, the distinguished head of the Royal Society. He sat facing the Prime Minister in the latter’s room at 10, Downing Street. Round the long table were grouped the members of the Cabinet. They were men who had lived through stormy and troublous times and had met stories of disaster without flinching. But, as they admitted afterwards, none of the terrible tidings of past years, when the fortunes of the Empire seemed to be tottering, had affected them to the same extent as the few brief words with which the distinguished savant summed up the long deliberations on which they had been engaged. They seemed pregnant with the very message of Fate. Almost they could see the writing on the wall.

“But, Professor,” asked the Premier, “do you really mean that nothing whatever can be done to check or prevent this terrible malady?”

“Nothing, so far as I am aware,” was the reply. “As you know the most distinguished men of science in England have been at work on the problem. We had a very full meeting last night, and the unanimous verdict was that the disease was not only absolutely incurable, but that nothing we have tried seems capable of affording even the slightest alleviation. The deaths reported already amount to nearly half a million; though the truth is being carefully concealed from the public in order to allay panic, yet practically every community in which the disease has appeared has been virtually wiped out. Curiously enough it does not seem to be spread by contagion. In spite of the rush of terrified people from districts in which it has appeared, no cases have shown themselves except in towns or villages where the mysterious violet cloud has been observed. That phenomenon has been the precursor of every outbreak.”

A month before, in the tiny village of Moorcrest, buried in the recesses of the Chilterns, an unoccupied house had suddenly collapsed with a slight explosion. No one was in the house at the time, and no one was injured. As to the cause of the explosion no one could form an idea. Nothing in the nature of the remains of a bomb could be discovered, and there was no gas laid on in the village.

But the few villagers who were about at the time spoke of seeing a dense cloud of pale violet vapour pouring from the ruins. On this point all observers were agreed, and they all agreed, too, that the cloud was accompanied by a powerful smell which strongly resembled a combination of petrol and musk. That was all the evidence that could be collected. No harm seemed to follow and the matter was speedily forgotten.

Very soon, however, the incident took on a new and sinister significance.

A week later a similar explosion took place in Ancoats, a poor and densely crowded suburb of Manchester. In every respect this incident duplicated the happening at Moorcrest. Naturally, it created something of a sensation, and the papers, recalling the Moorcrest mystery, made the most of it.

During the next fortnight similar explosions, all bearing the same distinguishing features, occurred in various parts of England. Sometimes there would be three or four in a single day in the same, or closely adjoining, areas. The public became excited. Not a single person was injured, the damage done was apparently trifling, since all the houses destroyed were of the poorest class. It looked like the work of a maniac—purposeless and without the slightest trace of a motive. People spoke of Bolshevists and Communists. But what Bolshevik or Communist, others asked, would waste time and effort to inflict such absurd pinpricks on Society?

They were soon to be undeceived. An enemy of Society was indeed at work armed with a weapon of a potency which far outstripped the paltry efforts of the Terrorists of old, to whom the bomb and the revolver were the means of world regeneration.

The explosion at Moorcrest took place on May 2nd.

Twelve days later, on May 14th, Doctor Clare-Royden, who was in practice at Little Molton, a village about four miles from Moorcrest, received an urgent message from an old patient summoning him to Moorcrest.

Doctor Royden, jumping on his motor-bicycle, answered the summons at once. A terrible surprise awaited him.

Practically every inhabitant of the village, about a hundred people in all, were in the grip of a fearful and, so far as Doctor Royden’s knowledge went, wholly unknown malady.

Its principal symptoms were complete paralysis of the arms which were strained and twisted in a terrible manner, fever which mounted at a furious speed, and agonising pains in the head. Many of the victims were already in extremis, several died even while the doctor was examining them, and in the course of a few hours practically everyone attacked by the disease had succumbed. The only ones to recover were a few children, too young to give any useful information.

It would be useless to trace or describe the excitement which followed, even though the Press, at the instigation of the Government, was silent upon the matter. Help was rushed to Moorcrest, the dead were interred and the living helped in every way. The Ministry of Health sent down its most famous experts to investigate. One and all admitted that they were completely baffled.

On May 21st Ancoats was the scene of an appalling outbreak of the disease. People in the densely packed areas died like flies. But there were some remarkable circumstances which drew the attention of the trained observers who rushed to the spot to inquire into the phenomenon.

Ancoats had been the scene of the second explosion twelve days before. It was not long before a health official noticed the coincidence that the outbreaks at Moorcrest and Ancoats occurred exactly twelve days after the explosions in each place.

The coincidence was, of course, remarked upon as somewhat suspicious, but it was not until it was reproduced in the terrible outbreak at Nottingham that suspicion became a practical certainty. It was speedily confirmed by repeated outbreaks in other parts of the country. In each case the mysterious malady broke out exactly twelve days after the appearance of the violet vapour. In all cases the symptoms were precisely alike, and the percentage of deaths was appalling. Neither remedy nor palliative could be devised, and the best medical brains in the country confessed themselves baffled.

By this time there was no room for doubt that the terror was the deliberate work of some human fiend who had won a frightful secret from Nature’s great laboratory. But who could it be, and what possible object could he have?

Leading scientific men of all nations poured in to England to help. For it was now recognised that civilisation as a whole was menaced; the fate of England to-day might be the fate of any other nation to-morrow. France and the United States sent important missions; even Russia and Germany were represented by famous bacteriologists and health experts. International jealousies and rivalries appeared to be laid aside, and even the secret service, most suspicious of rivals, began for once to co-operate and place at each other’s disposal information which might prove useful in tracking down the author of the mysterious pestilence.

On the day of the meeting of the British Cabinet, two men and a pretty, dark-haired French girl were keenly discussing the terrible problem in a small but tastefully furnished flat in the Avenue Kléber, in Paris.

“I know only three people in the world with brains enough to carry the thing out,” said the girl. “They are Ivan Petroff, the Russian; Paolo Caetani, the Italian, and Sebastian Gonzalez, the Spaniard. They are all three avowed anarchists, and, as we know, they are all chemists and bacteriologists of supreme ability. But I must say that there is not a scrap of evidence to connect either of them with this affair.”

The speaker was Yvette Pasquet, and there was no one in whom Regnier, the astute head of the French Secret Service, placed more implicit confidence.

“If the doctors could settle whether this poisoning is chemical or bacteriological it would help us a great deal,” said Dick Manton. “If it is chemical, I should be disposed to include Barakoff; he knows more about chemistry than all the others put together. But in any case, there is as yet nothing we can even begin to work on.”

A fortnight went past. The death-roll in England had assumed terrible proportions, and apparently the authorities were as far off as ever from coming to grips with the mystery. But a clue came through the heroism of a London policeman.

One night Constable Jervis was patrolling a beat which led him through some tumbledown streets in the lowest quarter of Canning Town. Suddenly he caught sight of a man rushing from a small empty house. At once Jervis started in pursuit of the man, who was running hard away from him. As he did so, there came the sound of an explosion, and the house the man had just left collapsed like a pack of cards. At the same time the odour of the dreaded violet vapour completely filled the narrow street.

The Terror had attacked London, and Jervis knew that to cross that zone of vapour meant certain death.

He did not hesitate. Muffling his face with his pocket handkerchief as he ran, he dashed at full speed after the stranger, whom he could just discern. He crossed the zone of death, almost overpowered by the curious scent of petrol and musk that loaded the still air, and a moment later was in pursuit, blowing his whistle loudly as he ran. A moment later a second policeman, hearing his colleague’s whistle, stood at the end of the road barring the way. The desperado was trapped.

Snatching out a revolver, the man backed against the wall and opened fire on his pursuers who were rapidly closing in on him. But both the policemen were armed, and both opened fire. Jervis’s second shot killed the man on the spot.

He proved to be a well-known member of a Russian anarchist group which had its head-quarters in the slums of Soho. The gallant Jervis had faced certain death—as a matter of fact he was among the hundred or so victims when the epidemic broke out twelve days later—but he had done his duty in accordance with the splendid traditions of the force to which he belonged.

The source of the mysterious epidemic was now, to a certain extent, localised. It needed no great acumen to guess the motive and origin of the fiendish plot. But to discover the master-mind which held the full solution of the mystery was another matter.

The first step was a general round-up of known members of the Anarchist Party. They were arrested by dozens, and very soon practically all who were known were under lock and key.

To the intense surprise of the police, one and all acknowledged that they were fully familiar with the scheme. Many of them had actually taken part in its execution. The secret had been well kept!

The explosions, it was learned, were caused by small bombs about the size of an orange. These were placed in the selected houses and timed to explode in a few hours. Evidently there was some defect in the mechanism of the one sent to Canning Town, and the man who placed it there must have seen that it was likely to explode prematurely and rushed in panic from the house.

But of the source of the bombs one and all of the men professed complete ignorance. They were, it was asserted, received by post from different places on the Continent. It was evident that the crafty scoundrel at the head of the terrible organisation took elaborate precautions to prevent their sources of origin being discovered.

But to have traced the outbreak to Anarchist sources was a step of the first importance. Immediately every branch of the secret service of the western world was concentrated on the problem.

A hint from one of the men captured, who collapsed under the cross-examination to which the known leaders were subjected, put the police in possession of one of the bombs. It had arrived by post the day before, and the miscreant to whom it was sent was caught before he had time to make use of it.

It was now possible to prove definitely that the disease caused by the bombs was chemical in its origin. Upon analysis the powder with which the bomb was filled was found to consist of a series of, apparently, quite harmless chemicals. A small portion fired by the detonator found in the bomb gave off dense clouds of the pale-violet vapour, and animals exposed to it were speedily killed, exhibiting every symptom of the terrible disease. Unhappily the secret of the detonator used defied discovery. The one found in the bomb had been used in the only experiment that had been made, and too late it was discovered that no fulminating material known would explode the apparently harmless powder.

“That seems to narrow it down to Barakoff,” said Dick Manton a few days later when Regnier brought them the news. “I don’t think either of the others is equal to research work capable of producing such results. Do you know where Barakoff is now?” he asked in French.

Regnier shook his head.

“He was in Moscow a year ago,” he replied, “and after that we heard of him in Prague, in Rome, and lastly in Madrid, but he disappeared suddenly and we have not been able to pick up his tracks again. He is a short, powerful, thickset man with a rather hunched back, but nothing else peculiar about his appearance.”

Next day, however, Regnier came to the adventurous trio in great excitement.

“Barakoff is in England!” he declared. “We have just had word from Gaston Meunier who saw him in Brighton a week ago!”

“But how on earth did he get there?” asked Jules. “You know every one has been looking for him for months past. He could not possibly have got through by any of the ordinary routes.”

“I’m as puzzled as you are, monsieur,” was Regnier’s reply.

“Well, if he is there we’d better go over,” said Dick. “Yvette can go with me in Mohawk II and Jules by the night boat. I shall fly the Mohawk to my old shed in Norfolk; I have kept it on in case of emergency, and it is quite safe.”

An hour later Dick was in close talk with a young Russian named Nicholas Fedoroff. He had been an active member of a circle of dangerous anarchists in Zurich, but had dropped out and was now living in Paris. By good fortune Dick had saved his baby girl, at imminent risk of his own life, from being killed by a motor-van in Paris, hence Fedoroff was impulsively grateful.

“Look here, Nicholas,” said Dick bluntly. “I want you to tell me anything you can about Barakoff.”

They were seated in a small café in the Rue Caumartin, which was Fedoroff’s favourite haunt. The Russian glanced round fearfully.

“Hush!” he said in broken French and in evident horror. “I—I can’t tell you! He has agents everywhere. If I were heard even speaking his name I should never get home.”

The man’s agitation was so pronounced that one or two men in the café glanced at him curiously. Dick saw that the mere mention of Barakoff’s name had thrown the Russian completely off his balance.

“Come to my flat,” he said quietly, “you have got to tell me.”

They drove in a taxi to Dick’s flat, where a stiff dose of brandy pulled the Russian together. Yet he still trembled like a leaf.

“How did you know that I knew Barakoff?” he asked.

Instantly Dick was keenly on the alert. He had no idea that Fedoroff had been associated with the notorious criminal; his appeal to Fedoroff had been a chance shot. Evidently he had stumbled on a matter of importance. But he was quick to take advantage of his good luck.

“Never mind how,” he said. “I do know, and that’s enough. You have got to tell me. I believe Barakoff is at the bottom of the trouble in England. I know he is there, and I want to know where he is and how he got there.”

The Russian’s agitation increased.

“You must not ask me; I cannot tell you,” he gasped.

“Then a few words from me in a certain quarter—not the police,” Dick suggested.

The Russian collapsed.

“No, no, I will tell you,” he moaned. “He is in England, but I don’t know where. He flew over.”

“Flew over!” echoed Dick in utter amazement. “Nonsense, he couldn’t have got in that way. Every aerodrome in England has been watched for months.”

“But he did,” the Russian asserted. “He has his own aeroplane. It makes no noise, and it goes straight up and down.”

Here was a surprise indeed! The secret of the helicopter with its almost unlimited power for evil was also in the hands of one of the most desperate ruffians in the world! There was indeed no time to be lost.

Fedoroff could tell Dick little more. What the secret of Barakoff’s influence over him was Dick could not fathom. He would say nothing, but evidently was in deadly fear.

One little item Dick did indeed extract and it was to prove valuable. Fedoroff knew that Barakoff had associates in Soho. And that was the only clue they could gain to his possible whereabouts.

That evening Dick, Yvette, and Jules crossed to England, and with official introductions from Regnier, Dick lost no time in getting into communication with Detective Inspector Buckhurst, one of the ablest men of Scotland Yard’s famous “Special Department,” a man whose knowledge of the alien scum which infested London was unrivalled. To him Dick told all he knew.

Buckhurst looked grave.

“I know of the man, of course,” he said, “but I have never seen him and I don’t think any of my men have. We have combed Soho out pretty thoroughly, but no one answering to Barakoff’s description has been seen.”

The position was very grave. If Fedoroff’s information was correct—and Dick saw no reason to doubt it—here was a desperate scoundrel lurking in England armed with an aeroplane of unknown design and power, and in possession of a terrible secret which, unless his career was brought to an end, threatened the entire population of the country. But where was he hiding, and, above all, where was his machine? Could it possibly be hidden, Dick wondered, in the very heart of London? The idea was almost incredible, but Dick knew Barakoff’s undoubted genius and his amazing daring.

A remarkable feature of Yvette’s personality was her wonderful influence over children. They seemed literally to worship her. She would get into conversation with the half-tamed gamins of the streets and in a few hours they would be her devoted slaves. She now proceeded to enlist the ragged battalions of Soho in a fashion that caused Buckhurst much amusement.

“Find out for me all the hunchbacked men you can,” was all the instructions she gave them.

“But, mademoiselle,” said Inspector Buckhurst, “it will be the talk of Soho, and our man if he is there will slip away.”

Yvette was unmoved.

“Just think a minute,” she said. “Who can go about all day and all night without being suspected? The children. Who can go into dens where your men hardly dare to venture? The children. Who know all the hidden haunts of which your men are utterly ignorant? The children. And finally, who are the most secretive people in the world? Again the children. Do not fear, Monsieur Buckhurst, they will not talk except among themselves, and that will do no harm.”

Buckhurst was far from satisfied, but he had gained such a respect for Yvette that he did not venture to override her. At the same time, he told her plainly that he should keep his own men busy. Yvette only laughed.

During the next forty-eight hours dozens of hunchbacked men were reported. Many of them were people whom not even the police knew. They were, of course, mostly harmless, but Buckhurst opened his eyes when one of them proved to be a notorious forger for whom the police had been looking for some months, and who had all the time been hidden under their very noses! Buckhurst began to feel a growing respect for the amazing French girl, who had beaten his smartest detectives on their own ground. But, unfortunately, none of the hunchbacks was the man they wanted, and at last they began to suspect that Fedoroff’s information was at fault.

Then came a dramatic surprise. One of Yvette’s small assistants, a sharp little Polish Jew boy, came to her with a strange story. He had been wandering about the night before and had seen a hunchbacked man let himself out of the side door of a big building half-way between Greek Street and War dour Street. The man had walked a considerable distance in a northerly direction into a part of London the boy did not know at all, and had entered an unoccupied house, stayed a few minutes, and come out again. The lad had shadowed him all the way, and had followed him homewards, until he again entered the building in Soho.

Dick, Jules, and Yvette turned out at once. The boy pointed out the building to them. It was a tall structure which dominated all the others in the vicinity. It was apparently a big shop with storerooms above. On the facia over the windows was the name “Marcel Deloitte, Antique Furniture.” There was nothing to indicate that it differed in the slightest degree from dozens of other shops and buildings in the neighbourhood. Yet Dick felt suspicious.

“We can do nothing till I get the Mohawk handy,” said Dick. “I will bring her down to-night.”

And he paused.

“I wish you would keep out of this, Yvette,” he went on wistfully. “It is going to be very dangerous, I am convinced.” The French girl was growing very dear to him, and he shuddered at the idea of her being mixed up in the coming struggle with a desperado of Barakoff’s type.

But Yvette shook her head.

“I’m in this to the finish, Dick,” was all she said in her pretty broken English, and Dick knew he could not move her. But he was full of fear.

That afternoon another explosion of the pale-violet vapour occurred in North London not far from Finsbury Park Station. Dick rushed to the spot with the boy who had followed the hunchbacked man, and the lad recognised the place without hesitation. The house destroyed was, he was confident, the one the hunchback had entered the night before.

Barakoff was located at last! But how was he to be captured? The problem was not so easy.

It was vital that, if possible, he should be taken alive. They knew what would follow the explosion at Finsbury Park, and there was a chance at least that if Barakoff were captured the secret of the disease, and possibly the antidote, might be wrung from him. If they could succeed in that hundreds of lives would be saved.

Together the three worked out a careful plan for the coup they intended to bring off next morning.

Very early a dozen street arabs were playing innocently close to the two entrances of the mysterious building. They were chosen specimens of Yvette’s band of ragamuffin detectives, and she knew that if Barakoff tried to escape he would have no chance of eluding their keen eyes. All the approaches were blocked by detectives, but Yvette insisted that none should approach the house itself. It was essential to the success of their plan that Barakoff’s suspicions should not be aroused.

From the roof of a big building half a mile away, Dick made a careful examination of what he was now convinced was Barakoff’s hiding-place. But he could see little. The roof was flat, but it was surrounded by a parapet practically breast high. There was obviously plenty of room to conceal a small aeroplane, but Dick could see nothing.

Dick and Buckhurst together saw the proprietor of the building from which Dick had made his observations. He readily consented to Dick’s plan, and towards evening placed a trusty commissionaire at the foot of the flight of steps leading to the roof with instructions that no one was to pass on any account whatever. Soon after dark the Mohawk dropped silently on to the flat roof. They were ready now to catch their bird!

In the morning Yvette, under the pretence of wishing to buy some old furniture, entered the shop. So far as she could see there was nothing suspicious. There was a manager, evidently a Russian, and two assistants.

Asking for a Jacobean chest which she did not see in the shop, Yvette was at length invited to the upper floors. These she found to be full of furniture.

Climbing the stairs to the third floor, accompanied by the manager, Yvette found herself in a large room divided in the centre by a wall, and with a door in the middle. Opening this door the manager bowed to her to precede him, and Yvette, quite unsuspectingly, obeyed. Next second the door crashed to, and she heard a key turn in the lock. She was trapped!

Before she could recover from her astonishment there was a rush of feet behind her, and she found herself seized in a grip which, as she at once recognised, it was far beyond her strength to shake off. She struggled frantically, but in vain. She was hopelessly overpowered and swiftly bound, and laid, gagged and helpless, on a sofa in the corner of the room. Then for the first time she caught sight of her captor. She recognised him at once. It was Barakoff himself! Worse still, he knew her!

The man was mad with rage, his face convulsed and his eyes blazing with fury.

“So, Mademoiselle Pasquet! We meet at last!” he snarled, stooping over her until his face was within a foot of her own and she could feel his hot breath upon her cheek. “But it is for the first—and last time!”

Accustomed as she was to danger in many forms, Yvette could not repress a shudder. In the power of a ruffian like Barakoff! She knew, of course, that at any moment Jules might become suspicious of her long absence and come in search of her. But how long would he be and what might happen in the meantime?

Barakoff set swiftly to work and fixed inside the doors heavy bars which, as Yvette realised with a sinking heart, would effectually shut out anyone trying to gain admittance, until either the door was reduced to splinters or a hole was knocked in the wall. Then he picked her up without an effort and carried her into the adjoining room. This, to Yvette’s intense surprise, was elaborately fitted up as a chemical laboratory, with all kinds of strange instruments and apparatus. It was evident that it had long been used for this purpose.

With an evil sneer Barakoff took from a cupboard what Yvette had no difficulty in recognising as one of the poison bombs! This he placed on a table and attached to it a short length of fuse. Then he began to busy himself with what seemed to be preparations for leaving, packing a few articles of clothing in a small bag and laying it down with a heavy coat beside it.

“When night comes, I go,” he said. “But you—you will remain. But I shall leave you in good company, mademoiselle,” and he pointed to the deadly bomb. “You will not feel dull. And after I am gone you will die—very slowly—of the twisted arms.”

For a few minutes the miscreant sat silent, smoking a cigarette and regarding Yvette with a look of triumph she found even harder to bear than the consciousness of her terrible danger.

Jules, on watch below, had at length become uneasy. He entered the shop and asked one of the assistants if the lady was still there.

“Yes,” replied the fellow readily, “she is upstairs with the manager looking at some furniture.”

Jules, his hand on his pistol in his pocket, and feeling strangely uneasy, started up the stairs. There was no one in the building. What could have become of Yvette and the manager?

On the third floor he noticed the door through which Yvette had gone. He seized the handle and tried to open it. But the door was locked and there was no key.

Not daring to raise an alarm for fear of the consequences to Yvette, Jules hastened down the stairs, and signalled to one of the Scotland Yard men. In a low voice Jules told him what had happened.

“We must be ready to break down that door at once,” he said.

With swift efficiency help was summoned, including a couple of men of the salvage corps, armed with powerful axes which would make short work of any ordinary door.

While the shop assistants were kept under surveillance, Jules and his helpers mounted to the third floor. They tried the door, and knocked. There was no reply, but inside they heard the hasty scurry of feet.

“Break it down,” said Inspector Buckhurst, who had been one of the first to arrive.

The salvage men sprang forward, and one on each side of the door began a furious attack with their axes.

Instantly a shot rang out. Splinters flew in showers, but the door, heavily barred and plated with iron, for a time defied all their efforts. At last it gave way, and headed by Jules the police party rushed in.

Their first discovery was Yvette, lying unconscious and bleeding profusely from a wound in the shoulder. Barakoff had fired at her as he hurried from the room when the thunderous attack on the door began. But in his blind haste his aim had been bad, even at such short range, and she escaped with comparatively slight injury.

But where was Barakoff?

Rushing out on to the flat roof Jules looked hurriedly round. To the southward a queer-looking aeroplane was just vanishing into the thin mist. But behind it, going “all out,” sped the Mohawk in furious pursuit. Dick Manton was taking a hand in the game of which he was a master! There could be but one end to that, Jules thought, with a sigh of relief as he turned to look after Yvette.

She was recovering consciousness and they were just about to carry her out, when one of the policemen with a loud cry dashed to the table. He had caught sight of a thin thread of smoke rising from the fuse of the bomb!

Luckily he was an old bombing instructor and knew what to do. A moment later the fuse was cut and the bomb’s detonator removed. It was harmless now. Half a minute later it would have exploded.

Watching keenly from his roof Dick Manton had seen Barakoff’s aeroplane rise swiftly and silently into the air. He had some slight trouble in starting the Mohawk, and the Russian was a mile away before the Englishman had started in pursuit.

Crouched in the driving seat of the Mohawk, Dick kept his eyes glued on the machine in front. He soon realised, to his dismay, that the Russian machine was much the faster and was leaving him behind. By the time they had gone ten miles and were out over the open country, he could only just discern the fugitive as a mere speck in the distance, and he realised with a sinking heart that a fleck of mist would enable Barakoff to escape.

Suddenly he discovered that the Russian machine had descended very low. A moment later it appeared to rise vertically, going up to a great height.

Instantly Dick followed and to his surprise found himself gaining rapidly. Then the Russian seemed to slip ahead again.

Several times this was repeated, and Dick at length divined the reason. The Russian could not run his elevating and driving propellers simultaneously. He travelled in a series of swoops, coming down very slowly as the machine drove forward, and then being compelled to stop the driving propellers while he gained the necessary height to continue his flight. No doubt this was explained by the fact that the planes were too small to keep the machine up without the elevating propellers.

Dick saw that he held a big advantage. The Mohawk, though slightly slower, could rise and go forward at the same time under the influence of both propellers.

As they sped over Kent, Dick began to realise with joy that he was gaining. Slowly the poison-fiend began to come back to him.

Then came the critical moment. Five hundred yards ahead and a thousand feet below, Barakoff, close to the ground, must rise soon to gain the elevation he required.

That was the moment for which Dick had been waiting. He called on his machine for the last ounce of effort he had been holding in reserve.

The Mohawk shot forward. A few seconds later Dick was directly above the Russian. So far as air tactics went he had won; the Russian was entirely at his mercy.

Then began surely the strangest aerial combat ever witnessed. To and fro the machines dodged, Barakoff striving to gain height and succeeding for a moment only to find his pursuer above him again and bullets whining round him; Dick striving to force the Russian down to the ground where he must either land or crash. For fully half an hour the machines flitted backwards and forwards around the town of Ashford. Dick had no fear of the result; his only risk was whether he could send Barakoff down before dusk came. Unless he could do this there was every danger that the Russian would escape under cover of darkness.

At last the end came.

Dick had forced his antagonist so low that, as a last desperate resort, Barakoff had to leap upward to clear a big group of elms. He miscalculated by a few feet, his machine touched the upper branches and went smashing to earth. Three minutes later Dick was standing beside the body of the death-dealer.

Barakoff’s machine was a complete wreck and was blazing furiously. The man himself had been flung clear and lay in a crumpled heap, stone dead.

There is little more to tell.

The formula for the powder with which the bomb was charged was found in Barakoff’s laboratory, and with it, in Russian, a prescription which, on being tested, proved to be a complete cure for the disease. It was found just in time to save those who would otherwise have been the victims of the explosion at Finsbury Park.

It was evident that Barakoff must have maintained his laboratory in Soho for months. Obviously the manager of the shop was one of his accomplices, and apparently he had recognised Yvette and deliberately thrown her into Barakoff’s hands. Then realising that discovery was inevitable he had slipped out of the building, probably by a window as neither of the assistants had noticed him leave. He was never found. The assistants themselves proved to be respectable young fellows who had been employed only a few weeks and who clearly knew nothing of the nefarious conspiracy.

Nothing but the Mohawk had prevented Barakoff’s escape! And Dick Manton received later on the official thanks of the British Government for his daring exploit.

Chapter Five.

The Master Atom.

“Oh! la la! How horribly dull life is! I do wish something really startling would happen, Dick!”

The words were spoken in pretty broken English by Yvette Pasquet, who, charming and chic, as usual, was sitting with Jules and Dick Manton. The adventurous trio were dining al fresco in the leafy garden of the old-world “Hôtel de France” on the river bank at Montigny, that delightful spot on the outskirts of the great Forest of Fontainebleau, a spot beloved by all the artists and littérateurs of Paris.

“Something will happen suddenly, no doubt,” Dick laughed, glancing at his beloved. “It always does!”

“I sincerely hope it will,” declared Jules in good English. “We’re really getting rather rusty. I met Regnier yesterday out at Pré Catalan with Madame Sohet, and he hinted to me that some great mystery had arisen; but he would tell me nothing further.”

“Regnier, as head of the Service, is always well informed, and like an oyster,” Yvette remarked with a laugh. “So I suppose we must wait for something to happen. I hate to be idle.”

“Yes. Something will surely happen very shortly,” said Dick. “I have a curious intuition that we shall very soon be away again on another mission. My intuition never fails me.”

Dick Manton’s words were prophetic, for on that same evening before a meeting of the Royal Society in London, Professor Rudford, the world-famed scientist, made an amazing speech in which he said:

“Could we but solve the problem of releasing and controlling the mighty forces locked up in this piece of chalk, we should have power enough to drive the biggest liner to New York and back. We should have at our disposal energy unlimited. The daily work of the world would be reduced to a few minutes’ tending of automatic machinery. And, I may add, the first nation to solve that problem will have the entire world at its mercy. For no nation, or combination of nations, could stand even against a small people armed with force unlimited and terrible. And—gentlemen—we are on the way to solving that problem!”

As the words fell slowly and calmly from his lips his hearers felt a thrill of ungovernable emotion, almost of apprehension. For they knew well that he spoke only of what he knew, and the measured phrases conjured up in their keen brains not only a picture of a world where labour had been reduced to the vanishing point, but of a world where evil still strove with good, where the enemies of society still strove against the established order of things which they hated, where crime in the hands of the master criminal, armed with force whose potentiality they could only dream of, would be something transcending in sheer horror all the past experiences of tortured humanity.

Supposing the great secret fell into the wrong hands!

The speech at the Royal Society was a nine days’ wonder.

The unthinking Press made merry in the bare idea of a lump of chalk being a source of power. Then the transient impression faded as public attention returned to football and the latest prize-fight. But behind the scenes, in a hundred laboratories, students bent unceasingly over their myriad experiments, striving to wrest from Nature her greatest secret, the mystery of the mighty energy of the atom. Since the day when Madame Curie had discovered that in breaking up, yet seemingly never growing less, radium was shooting off day and night power which never seemed to diminish, the minds of the men of science had been filled with the dream of discovering the secret.

Could they learn to accelerate the process? Could they induce radium to deliver in a few moments the power which, expending itself for centuries untold, never seemed to grow less? Could they learn to control it, or would it, when at last the secret was discovered, prove to be a Frankenstein monster of titanic power, wreaking untold destruction on the world?

A thin, keen-faced man sat facing the British Prime Minister in his private room in Downing Street a few days later. This was Clinton Scott, one of the smartest men of the British Secret Service, a man of wide culture and uncanny knowledge of the underworld of international crime. His profession was the detection of crime; his hobby science in any form.

“We have very disturbing news, Scott,” said the Prime Minister, “and I have sent for you because the problem before us is largely of a scientific nature and I know all about your hobby.”

Clinton Scott smiled.

“You are aware, of course, of the latest developments in the search for some method of releasing and controlling atomic forces,” went on the Prime Minister. “I do not profess to understand them deeply myself, but I have a general idea of what is being done and what success would imply. Professor Rudford, to whom I applied for information on the subject, tells me that such a discovery would revolutionise world conditions. You will understand of your own knowledge all that it implies, and that is why I have sent specially for you in this matter.”

“I am at the country’s service,” replied Scott.

“Now information we have received from Norway suggests very strongly that the problem has been solved,” the other said. “We have no details—nothing in fact very definite at all. But it is certain that some very queer things have been happening. And from what Professor Rudford tells me I am assured that we cannot afford to neglect them. Our ordinary men are useless for this kind of thing. Men with a considerable knowledge of scientific subjects are absolutely necessary. Otherwise matter which, properly understood, would be full of significance will be passed over as of no account and quite minor and unessential incidents will be followed up, and there would be serious waste of time. And time is valuable.”

“I agree that it is,” was the terse reply.

“I want you to go to Norway and look into the matter,” the Prime Minister went on. “Of course I will see that you get all the information we have, and you can select your own assistants.”

Clinton Scott suddenly looked grave.

“Is it known at all?” he asked. “Who is behind this—I mean who has made this discovery? You will appreciate my reason for asking. If it is the work of a genuine man of science there would be no immediate danger, though of course such an invention would upset all ideas of international relations. It is literally true, as no doubt Professor Rudford will have told you, that the nation in exclusive possession of such a secret could dominate the world. But there are one or two men in the world who, with such a secret in their possession, would be a real peril to civilisation.”

“Do you know a man named Lenart Gronvold?” asked the Premier.

Clinton Scott started visibly.

“Do you mean to say he is in it?” he gasped in utter astonishment.

It was the Premier’s turn to be surprised.

“Why—who is he?” he asked. “Professor Rudford had never even heard his name and laughed when I suggested that he could have had anything to do with it.”

“He won’t laugh when he gets some real idea of Gronvold’s ability,” said Scott bitterly. “The man is one of the mysteries of the world of crime,” he went on. “Exactly who he is we don’t know—I mean we know little about his life. But we believe he is Norwegian born, though he has strong Russian characteristics. We know he studied at Leipzig. Tutors who knew him well speak with the utmost admiration of his amazing brain power as a student and the daring of his conceptions. But for some reason he never did well in examinations and attracted no attention whatever outside a very limited circle. Personally, I believe that for some strange reason he deliberately elected not to call attention to himself, for there is not the slightest doubt that he could with ease have captured every honour the University had to bestow. After leaving Leipzig he disappeared for some years. I don’t know how he spent them. But I do know that he is a chemist of amazing ability. He has, moreover, been mixed up with a number of puzzling international crimes, though we have never been able to bring any of them home to him. Do you remember the big bank robbery at Liverpool three years ago?”

The Premier nodded.

“You mean,” he said, “when the bank vaults were blown open with dynamite and half a million in gold stolen?”

“That’s the case,” said Scott. “Only it wasn’t dynamite, there was no explosion. The thick steel and stone walls of the vaulted safe had been melted through as if they had been butter. The story of an explosion was deliberately given out to deceive the thieves. But the fact is that some process was used of which we have no knowledge whatever.”

And he paused, then went on:

“Now I am pretty sure Gronvold was in that. I was called in before anything had been touched. And in one corner I picked up a scrap of paper bearing some queer formulae of which I could make nothing. It had evidently been dropped by accident. And it bore Gronvold’s name. Moreover, as I ascertained by a visit to Leipzig, where I saw some of the old University registers, it was in his handwriting. But where he is, how he got into England, how the burglary was effected and how he got away with such an enormous weight of gold we never could make out. If he is really in this new discovery we are face to face with a terrible problem. The man is absolutely without scruple, and for three years he has had the use of half a million of money for his experiments. He may have done anything in that time.”

“But how did you know of him?” asked the Premier.

“It’s a queer story,” replied the other. “Simmons, one of our men in Christiansand came across, quite by accident, a drunken Norwegian sailor who told a strange story of the blowing up of a mountain by a tiny cartridge placed at the bottom of an old mine shaft. He actually mentioned Gronvold’s name, and claimed to have been one of his assistants. When he became sober he was evidently terribly alarmed at having talked, and denied the whole story. The same day he disappeared, and Simmons has been unable to trace him.”

He went on after a pause:

“Now the blowing up of a mountain is a fact. A hill nearly a thousand feet high in a wild lonely district north-east of Tonstad has absolutely disappeared—levelled out. To have done the work by ordinary means would have meant years of labour and would have cost a fortune. There can be no doubt that some entirely new force has been employed. Officially the occurrence is attributed to a landslide; actually it is and can be nothing of the kind. Now this, coupled with what the Norwegian sailor said, suggests that we ought to look into the matter. Whether the Norwegian Government knows anything about it I do not know, and the matter would be of such importance from the international point of view that we cannot make direct inquiries.”

“Will you take it in hand?” asked the Premier. “Whom will you get to help you? I am afraid the ordinary men would be of very little use.”

“I think I will run over to Paris and see Regnier,” replied Scott. “He has a fellow named Manton who will certainly be useful. He was in our flying corps and was invalided out owing to wounds. He has done some wonderful work and has an entirely new type of aeroplane which he invented and which, by the way, our people would have nothing to do with. Regnier swears by him. He works always with a French girl named Yvette Pasquet, who did some splendid intelligence work during the war, and her brother Jules. They will have nothing to do with anyone else when they are on a case, and they have had some amazing results.”

Crossing to Paris by the afternoon air express Scott the same evening was warmly greeted by Regnier. He rapidly explained his visit. Regnier looked grave.

“I have heard of the man,” he said, “but have never seen him, I don’t think in a case like this you can do better than Manton. He is very well up in all these scientific things; they seem to be a perfect craze with him.”

An hour later, Regnier, Scott, Dick Manton, Yvette, and Jules were closely discussing the problem in Manton’s rooms.

“We have got to find that sailor,” was Dick’s verdict, “and luck is going to have a good deal to do with it. I suppose Simmons is on the look out for him?”

“Yes,” replied Scott, “I wired him at once.”

“Do you think Gronvold and the sailor have quarrelled?” put in Yvette.

“I think not,” was Scott’s reply. “If they had there seems no reason for the man’s alarm. I think he calculated on going back to him. That was Simmons’ view, too.”

Dick, who had been carefully studying a map, looked up.

“Just look here,” he said, “you could hide an army in this place.”

The map was in contour and gave a vivid impression of the wild and desolate country, a broken mass of hills and lakes, stretching north and east from Tonstad.

“Suppose Gronvold is there,” said Dick, “he could hide anything he wanted to. I don’t think he would have travelled far from its base to blow up the hill—that was probably experimental. My idea is that he has established his laboratory somewhere in the hills about there. There is no population and little or no traffic through the district. He must send to one of the towns for supplies, and Christiansand is the most likely. I should guess that the sailor had come there for that purpose and may come again.”

“He did not leave the town by boat,” declared Scott. “Simmons made the most careful inquiries on all the boats in the harbour and no one of his description was seen.”

Three tourists a week later were lodged in a comfortable hotel in the Dronningens Gade, one of the principal streets in the busy port of Christiansand. They were Yvette, Jules, and Scott. Dick had flown the Mohawk direct to the wild district north-east of Tonstad, and with the help of a light tent had pitched a camp in a little wood a couple of miles from the southern edge of the blown-up hill. He had taken pains in the selection of a suitable place and his camp and the Mohawk were so admirably hidden that they were safe from discovery, unless some one actually walked right up to them, a contingency which in that roadless, unpopulated country was extremely unlikely. But though hidden himself he commanded a wide view.

For two days Dick devoted himself to a thorough examination of the surrounding country, quartering it thoroughly either on foot or in the Mohawk. He could however see nothing in the least suspicious.

Then came a surprise.

His only method of receiving news from the others was to “listen in” on the wireless telegraph set with which the Mohawk was fitted for messages which, directed to an address in England, were handed to the Christiansand radio station for dispatch, but were really intended for him. These messages were handed in at eight o’clock precisely and Dick usually got them within half an hour.

On the third day of his watch came the message:

“Sailor located. Travelling north with pack mules. We follow. Osterluis road.”

The man, as he was to learn later, had been spotted by Yvette in Christiansand. She had seen him leave a small café much frequented by sailors, and had been struck by his likeness to the description given by Simmons. She had followed him for some time while he made a variety of purchases at numerous shops, and had been struck by the fact that a mere sailor should evidently have such a large sum of money at his disposal. Luckily she had encountered Simmons, who at once recognised the man and had promptly disappeared to avoid arousing his suspicions.

Yvette was able to learn that all the man’s purchases were being delivered to a small inn on the outskirts of the town, and a few inquiries showed that he had four mules stationed there.

The matter began now to clear up. They were sure of the man; at least he could not leave without his mules and stores. Jules and Scott took up the watch at the inn, while Yvette shadowed the suspect. It was thought best that Simmons should not appear. It soon became evident that the man had no associates in Christiansand. All he did was to visit shops, paying cash for all his purchases and having them sent to the inn where his mules were stabled.

The next day, with his mules heavily loaded, he set out from Christiansand, taking the road to Trygstand and Ostersluis.

Yvette, Jules, and Scott decided to follow him on foot. To have taken horses would have told him he was being followed as soon as he left the road, as they were pretty sure he would, sooner or later. Luckily all three were splendid walkers and felt they would have no trouble in keeping up with the heavily-laden mules. Cramming a few necessities into rucksacks they were soon on the track of their quarry.

Man and mules made steady progress. They were soon through Trygstand and, shortly after, caught sight of the Mohawk high above them and evidently following the road on the watch for them.

With a handkerchief tied to a stick Yvette swiftly signalled to Dick the brief facts, and the Mohawk passed on towards Christiansand. When the sailor and the mules were hidden in a dip in the road Dick landed, and all four held a brief consultation as to their future plans.

As a result Scott put on his best speed and soon passed the sailor who had stopped for a rest. The man was now between two parties on the ground and under observation from Dick from the air. He certainly could not escape.

A few miles beyond Trygstand he suddenly left the high road, and turned westward and north across the open country. Evidently he was not bound for Ostersluis. But where could he be going? For miles there was not even a house in the deserted track of country into which he had plunged.

But it was evident he knew his bearings thoroughly. Hour after hour he jogged along, and soon the pursuers realised that they had been wise not to bring horses. No horse could have crossed the country over which the sure-footed mules went swiftly without a stagger.

At nightfall the man camped. Apparently he paid no attention to the passing of the aeroplane, for he barely glanced at it. Building a small fire under the shelter of a rock, the three pursuers spent a comfortless night. Dick had flown to his camp, intending to pick the party up again at dawn.

Early next morning the man was afoot and continued his journey. He was now in the wild country well to the west of Ostersluis, and travelling due north. Yvette, Jules, and Scott were a mile behind, following with the utmost care not to reveal their presence and so rouse the man’s suspicions.

They had gone but a few miles when the man paused on the flat top of a high hill, which on the side away from them sloped steeply into a deep gorge at the foot of which ran a small stream. They watched him narrowly.

With great care he got the four mules together, standing side by side. He himself took up a position directly in front of them and almost touching the animals’ heads.

A moment later man and mules sank together, apparently into the earth and disappeared!

They could hardly believe their eyes! Surely the man must have gone down the reverse slope of the hill. But they were confident that he had not moved.

They hurried to the spot. Not a sign of any living thing was to be seen! The mystery was profound.

While they stood gazing at one another in speechless amazement, the Mohawk, which they had not perceived above them, dropped vertically downwards and landed a few yards away. Dick sprang out.

“Did you see?” he gasped. “The man and mules went down into some sort of pit. But where was it?”

The flat top of the hill was broken into a series of narrow cracks; apparently the rock of which it was composed was of volcanic origin. They examined it closely, but they could discover nothing which offered a solution of the mystery.

Dick described closely what he had seen from the sky. It agreed with what the others had observed. The man had got the mules together, and all had sunk slowly downward. Dick had seen the black mouth of the pit for a few moments and a blaze of light. Then the pit had disappeared, and the ground resumed its normal appearance.

“We shall have to camp here to-night,” said Dick. “We must get to the bottom of this. We shall have to take turns to watch. In the meantime we had better have a look round.”

Having closely examined the top of the hill, they turned to the deep gorge and descended to the bottom. The stream, they found, issued from the hill itself, flowing out from a low tunnel high enough to admit the passage of a man. From it also issued a cloud of mist which spread over the bottom of the little valley in a thick blanket which completely concealed the surface of the ground from anyone at the top of the hill.

But still more remarkable was that the bed of the little stream was deeply covered with what appeared to be recently melted lava. In many places it was still hot, and the water, they found, was nearly boiling. The first traces of this were found at the mouth of the tunnel from which the stream emerged, and for hundreds of yards the molten rock could be traced, as though it had poured from the tunnel and flowed down the bed of the brook.

Wood and water were available in abundance, and soon they had pitched their camp, near enough to the top of the mysterious hill to enable them to watch it closely and yet well concealed so that if the man reappeared they would have no difficulty in escaping observation.

The first watch fell to Yvette, and with a revolver ready for instant use, she prepared to spend a couple of lonely hours on the edge of the hill. The camp was but a quarter of a mile away so that a shot would bring her speedy help at any time.

A brilliant moon lit up the country for miles.

There was no trace of any living thing. Everything was still and silent.

Yvette had been on watch about an hour when she became aware that the air was full of a dull murmur of sound. She listened intently. There was no mistake about it. A dull throbbing noise was distinctly discernible.

She walked round the flat top of the hill, looking keenly in every direction and trying to locate the position from which the mysterious sound was coming. But it was in vain.

Glancing into the gorge, she saw a strange and terrible phenomenon. The course of the little brook was traced in a dull fiery glow. Clouds of steam were rising thickly into the night air; she could plainly hear the sharp hiss of water on something hot.

She ran swiftly down the hill. At the bottom she paused on the edge of the stream. The water had disappeared and in its place ran a river of molten rock! Through her boots she felt the heat of the ground.

Returning to the top of the hill she waited for Dick, who was now almost due to relieve her. In a few moments he appeared and listened in amazement as she gasped out her story.

The dull, throbbing noise was still audible.

“Machinery,” said Dick laconically, “but where?”

Suddenly he flung himself on his face, and pressed his ear close to the ground.

“Listen,” he said.

Yvette followed his example. There could be no mistake; the mysterious sound was coming from the ground beneath their feet! The earth was full of muffled thunder.

Dick took from his pocket a hammer and struck a sharp blow on the flat rock beneath their feet. It rang hollow! Unmistakably they were standing on the roof of a cavern.

Walking to the camp they roused the others and told them what they had seen and heard.

“We have got to catch that sailor if we wait here a month,” said Scott. “He must come out again some time. But how about food?”

“We have enough tinned stuff in the Mohawk for a week,” said Dick, “so we shall be all right for a few days. In the meantime we must watch the place closely.”

Next day passed without incident until evening was drawing on. Then Yvette, who was watching the top of the hill while the others rested, at six o’clock gave a low whistle. She was lying on the ground keeping observation between a couple of rocks which hid her completely. In a moment the others had crawled to her side.

“Look!” she said.

On the top of the hill, three hundred yards away, stood the sailor and the four mules, clearly silhouetted against the evening glow. He had appeared suddenly, Yvette told them, just on the spot where he had disappeared on the previous day.

“We must get him,” said Dick.

The man with the mules started to return along the way he had come. They saw at once that the path he was taking would bring him close to them.

With the mules unloaded the man evidently had no intention of walking. He mounted one of the animals and rode towards them at a fast trot.

He was within twenty yards when Dick aimed his revolver and fired. The mule the man was riding bolted, throwing its rider heavily. Before he could recover himself he was bound and helpless. The other three mules stampeded wildly and were soon out of sight.

Carried to the camp the man soon recovered. But he resolutely refused to say a word.

“Well,” said Dick. “We must try to get into the cave. Perhaps the tunnel out of which the brook runs will lead us to it.”

They were soon at the mouth of the strange tunnel. There was no sign of the molten matter of the previous night. The stream, thick with mud, flowed sluggishly, but the water was cool, and the ground, which the night before had been too hot to walk upon, was now not more than uncomfortably warm.

With Dick leading, Scott and Yvette next in order, and Jules bringing up the rear they entered the mouth of the tunnel. There was, they found, just room for them to pass, stooping low and walking knee deep in the little stream. They were, of course, in total darkness, for Dick was afraid to show a light for fear of betraying their presence.

For a hundred yards Dick groped his way onward. Then his outstretched hands struck something soft. It was a kind of curtain hung across the stream, thick and heavy.

Cautiously he slightly raised one corner and peered through. The sight that struck his eyes filled them with amazement.

They were at the entrance to an enormous chamber, a hundred and fifty yards across, dimly lighted by a single big electric lamp, the only one alight out of dozens which hung from the roof. The floor sloped steeply upwards at the far end where they could make out a kind of platform, reaching nearly to the roof and with steps leading downward into the great hall. All round the side were a series of openings, apparently small chambers cut into the solid rock. From one of these the stream they had followed seemed to issue, crossing the floor of the great cave in a narrow deep channel.

But what fascinated Dick’s attention was a great table, apparently of iron, which occupied the centre of the cave. It was heavily constructed and seemed to be based on massive legs which went down into the rock. Upon it stood a strange machine unlike anything he had ever seen before and of the use of which he could not form the smallest idea. Surmounted by two huge governor balls, it was a complicated mass of polished wheels, of some metal which Dick could not identify, and which gleamed with a strange radiance in the light of the huge electric lamp overhead. From the machine a bewildering mass of wires led to a series of points at the face of the rock.

So much Dick could make out in the dim light. He was keenly anxious to learn more. But how was it to be done? No sign of any human being was to be seen, but he could not imagine that what lay before their eyes was the work of the solitary sailor who now lay bound in their camp.

At any rate they could not remain where they were. Dick decided to try to gain entrance to one of the wall chambers where they could shelter with a better chance of seeing what would happen in this underground home of mystery. But which should they choose?

Some of the chambers were half-way to the roof and were reached by steps cut in the solid rock. Dick decided on one of these not far from where they were standing. They crept cautiously from their hiding-place and stole along to the bottom of the cave. A moment later they were at the foot of the steps. These they hastily climbed, and soon found themselves in a fair-sized cave, fifteen or sixteen feet above the floor of the main cavern and commanding a good view of the entire area. It was dry and warm and formed an ideal post of observation, provided their presence remained undiscovered.

Suddenly a blaze of light struck their eyes. Some one had turned on the whole of the electric lamps which hung in clusters from the roof.

Peering cautiously out they saw, to their amazement, half a dozen men issue from different chambers near the floor of the cave. All wore big round spectacles of deep blue glass and were clothed in close-fitting garments of rubber, with heavy gauntletted gloves of the same material. Apparently they could not see well, for the spectacles must have been almost impervious to ordinary light.

One of the men, fixing his spectacles on more firmly and, drawing his rubber overall more closely around him, approached the strange machine which stood on the table. The others proceeded to the points at which the wires from the machine reached the side of the cave. Here they took up some kind of tool which looked like a gigantic blowpipe and stood ready as if awaiting a signal.

A low whistle sounded from the man at the table, as he grasped a small wheel and gave it a quick turn.

An instant later an appalling blaze of light burst from the strange machine, and the cave was filled with a roar of sound, a terrible deep drone of such frightful intensity that the hidden watchers shuddered as if with actual physical agony. Dick felt the sweat start suddenly from his forehead and pour down his face. Anxiously he glanced towards Yvette. She lay with her face buried in her arms, her body trembling convulsively. Scott and Jules, their faces white as chalk, were gazing at the unearthly light which streamed from the whirling machine, shading their eyes with their hands to shelter them from its blinding radiance. They could not look at it for more than a few seconds; it was like trying to gaze at the sun at midday.

Taking a letter from his pocket, Dick bored a tiny hole in it with his scarf pin. Through this hole he found he could see in comparative comfort. He signed to the others to do the same, and soon all four—for Yvette quickly recovered her self-possession—were eagerly watching the strange scene before them. Speech, in the deafening noise by which they were surrounded, was, of course, out of the question.

The man at the great table in the centre of the cavern evidently had a task of great difficulty to control the movements of the strange machine, which he seemed to do by means of a large wheel something like the steering wheel of a steamer. Long streamers of flame shot from it in all directions, and as its mass of wheels revolved at terrific speed it shook and trembled as if it would actually leap from the table.

In the meantime the men at the rock face were hard at work with big blowpipes, from the muzzles of which shot streams of fire of such intensity that the solid rock seemed to melt away like butter. The molten matter was led by ducts in the ground through a grid of some metal, evidently highly refractory to heat, for it appeared to do no more than glow white-hot even in the terrific temperature of the melted rock. After passing through this grid the molten matter was led to the bed of the stream, from which the water had in some manner been cut off, and flowed out the way Dick and his companions had entered.

What was the object of the work?

Dick could not guess, but every now and again one of the men would walk to the grid and with a long implement shaped like a hoe would scrape off something adhering to the bars, which he deposited in a big tank of water. Dick determined that, sooner or later, he would obtain a specimen.

But in the meantime their position was decidedly precarious. If they were observed there was no possible way of escape, for the tunnel by which they had entered was barred by the stream of molten matter. They could only lie still and hope that no one would enter the gallery in which they lay concealed.

After two hours of work, the man at the table stopped the machine, and all the men straightened out for a rest. Evidently they were very much exhausted. The lights were extinguished, except for the single one which was burning when they entered, and the men returned to their quarters, evidently almost falling with weariness. Dick came to the conclusion that they could only carry on the work on which they were engaged for a short time and that after that sleep and rest were imperative. The flow of molten metal had stopped and the water was again allowed to flow along its ordinary channel, from whence it sent up huge clouds of dense steam.

This gave Dick his chance.

Sending the others to the mouth of the exit, he cautiously crept towards the tank in which were deposited the scrapings from the grid which filtered the molten rock. He reached it safely, and plunging in his arm up to the shoulder, abstracted a couple of handfuls of what seemed like heavy shot. These he placed at once in his pocket.

He was about to return to the others when his attention was caught by the queer platform at the one end of the cave. Looking at this carefully he found that it was really a huge lift, and at once the mysterious disappearance of the sailor and the mules was explained. It was evident that the top of the lift was really the thin covering of rock which had sounded hollow when tapped and that this had been so cut that when the lift forced it into position only traces of ragged crevices were left on the surface. Dick could not but admire the ingenuity with which this approach to the subterranean retreat had been devised.

Presently he heard a heavy knocking above his head and, guessing the cause, shrank back for shelter into the mouth of a small cave adjoining. A moment later a man emerged from one of the other chambers and approached the lift. Dick was curious to see how it worked. There was, as he could see, a small electric motor fitted to it, but where could the necessary power come from?

The new-comer carried in his hand a tiny machine which was in every respect a duplicate in miniature of the big one on the central table. But it was so small that the man carried it easily in one hand. From it ran a pair of electric cables which the man proceeded to connect with the terminals of the motor.

Placing the machine on the ground he gave the wheel a sharp turn. Immediately the tiny machine began to revolve, throwing out flashes and flames exactly like the larger one but on a miniature scale.

Clearly, however, there was considerable power in it, for the lift at once commenced to descend. On it stood a man whom Dick instantly recognised as Gronvold. And he was accompanied by the sailor whom Dick had left safely tied up in their camp. Evidently Gronvold had found and released him.

Their position was now indeed one of terrible gravity.

As soon as the lift reached the bottom the two men stepped off and the lift reascended, moving upward with an ease which showed the tremendous power developed by the tiny machine. Here, indeed, was something of which Dick had had no previous experience.

The three men crossed the cave to the shelter occupied by the man who worked the big machine, who was evidently the captain, and Dick knew there was no time to be lost.

Directly the men entered the shelter, Dick dashed across the cave to join the others, snatching out his revolver as he ran.

He had nearly reached them, when a whistle blew and instantly half a dozen men rushed from different caves. They were discovered!

“Take care of Yvette, Jules!” Dick yelled as, with Scott at his side, he faced round to the men who were rushing at them from three sides.

Instantly Yvette and Jules plunged into the tunnel. Dick and Scott backed after them with drawn revolvers threatening the men in the cave.

For a moment the leaders hesitated; apparently they were not aimed. Then Gronvold rushed to the front, followed by the captain, both carrying curious weapons which looked like heavy pistols.

All four men fired simultaneously. Dick saw the captain drop, evidently shot dead, and heard a bullet whiz past him and strike the rock behind. A burst of flame singed his hair, and he felt the hot breath of it on his face.

Then Gronvold fired at Scott. The effect as the bullet struck him was strange and awful. His body actually disappeared in a mass of flame under the impact of some projectile of unimaginable power and energy. At the same instant Dick slipped on a projecting bit of rock and fell heavily on his head. As he lost consciousness he heard the crack of a revolver behind him. Yvette and Jules, hearing the shots, had returned in the nick of time. Jules snatched up Dick and carried him down the tunnel, while Yvette very coolly shot down Gronvold just as he was reloading his terrible weapon.

When Dick recovered his senses he found himself lying on the ground at the entrance to the tunnel, his head pillowed on Yvette’s arm as she tried to pour some brandy between his lips. He could feel the sobs which shook her, and even felt a tear on his face. Jules stood on guard at the entrance to the tunnel, his revolver ready for instant action in case of pursuit.

As Dick opened his eyes, Yvette gave a gasp of relief.

“Oh, dearest, I thought you were dead!” she sobbed and burst into tears. A moment later she turned away blushing scarlet. She had betrayed her secret at last. And even in his confused state Dick felt a thrill of triumphant joy.

His head spinning he staggered to his feet. But he would have fallen if Yvette had not caught him.

“Sit down, Dick,” she said peremptorily. “Jules can look after this place.”

Dick obeyed, perforce; he was so sick and giddy that he could have done nothing even if the expected attack had come.

But it never came. Suddenly as they stood there, tense and waiting, a terrific convulsion shook the earth. With a terrible roar the great cavern collapsed and a vast burst of smoke and flame vomited to the sky, and a deep crater was left by the subsidence. Sick and dizzy, with showers of stones falling all around them, they stood aghast while explosion after explosion rent the air, rendering the crater deeper. It was some minutes before quiet reigned again and, white and shaken, after their nerve-racking experience, they were able to collect their shaken faculties and make an examination of the scene.

The hill beneath which the cavern was located had practically disappeared; in its place was left nothing but a heap of torn and tumbled earth and rock. Its dreadful secret was safe, for the cave and its contents, and the men who had wielded such titanic forces, were buried deep under tens of thousands of tons of débris.

Perhaps it was as well, Dick thought. There are some forms of knowledge which mortals ought not to possess; there are some powers which they are not fit to handle.

Whatever secret Gronvold had discovered, it rested with him for ever on the very scene of his ill-omened labours. What had gone wrong in the depths of the cavern they could not even imagine, but it was evident that the mysterious force which Gronvold had called into existence, whatever it was, had destroyed him and his companions. And it was almost by a miracle that Dick, Yvette, and Jules had escaped.