Chapter IV: Part 4

"Ja! ja!" replied the other as he strained his eyes in the attempt to decipher the handwriting on the half-burnt sheet. "But I cannot understand it, for it is in a foreign language."

"It is part of a small fragment of an envelope, and the writing, which is in English, is certainly almost undecipherable, but I can distinguish the letters '...eane'."

"Ach, Himmel! That is Keane!" replied Strauss. "He is one of the aerial police, is he not?"

"You are right, Fritz. This letter was addressed through the English post to Captain Keane, one of Tempest's best men, if not indeed his most brilliant 'brain-wave,'" hissed the professor.

"Donner und blitzen! Then he has come here to search for the _Scorpion_, and the aerodrome."

"Yes, but look, he only left London a few hours ago, for here is the London postmark in the corner, bearing yesterday's date."

"And his companion? Who is he?" asked the mechanic.

"It must be that other scout pilot, Sharpe; they work together. But, mark my word, Friedrich Strauss, they are mistaken if they think to find an easy victim in Professor Rudolf Weissmann. I'll teach them to track me like a murderer through the Schwarzwald. They have come to the Black Forest, and here they shall stay." And for once, the quiet, mild-mannered professor jerked out his words with unusual vehemence.

The mechanic saw that his chief was deeply agitated by this sudden discovery, which confirmed all his recent fears, and to allay his feelings, he said,

"But they will never find the aerodrome, Professor, or, if indeed they find it, they will never enter it alive; think of the preparations you have made for all uninvited guests," and the speaker shuddered, for he knew something of the terrors of that "death-circle" in the lonely forest.

"Bah! it is my secret they want, the secret of that mysterious power which drives the _Scorpion_."

"Uranis?" ventured the other.

The professor nodded, for he regarded it as the greater success of the two. Without it the _Scorpion_ would be useless; with it a dozen _Scorpions_ could be built, once the facilities were provided. Unfortunately the discovery had been effected too late to win the war for the Fatherland. Besides, he had not received the encouragement from the government that he had deserved, and his soul was consequently embittered.

"Come," he said at last, "we must get back to the aerodrome and watch for these half-witted Englishmen. Once there we can afford to laugh at them. They will soon be held in a vice. But I must send a further message to the _Scorpion_ out on the Hamadian plains, hinting how matters stand. After that communications may have to cease for a while. As for these death-hunters, they will find out presently that they are up against something far more terrible than anything which old Jacob Stendahl or the wood-cutter have ever imagined in their wildest fancy. The secret of the Schwarzwald is not for them. I hold the master-key, Fritz, and when I die that master-key will be broken."

And the two men, who had been aware of the presence of the Englishmen ever since they entered the forest, and had watched them accordingly, now moved off in the same direction which the latter had taken half an hour before.

*CHAPTER XVIII*

*"LIVE WIRES"*

Matters in the Schwarzwald were now rapidly nearing a climax; the final contest between German brains and English wit could not much longer be delayed. For the moment Keane and Sharpe, unknown to themselves, were enmeshed in the network of a deathly trap. Nothing less than a miracle, or something approaching the same, could now set them free from their perilous position. One thing was certain, and that was that this clever but unscrupulous mathematician and engineer, who was now their declared enemy, would not hesitate to adopt the most extreme measures to get rid of his unwelcome visitors. Unfortunately his power, which almost approached the supernatural, made him a dangerous and a wily foe.

It was now past midnight, but the two Englishmen, who had left the track some time before at a point where its course was suddenly changed, and had continued their journey by the aid of a luminous compass, and the uncertain light of the moon, came at last to another halt.

"Let us stay here a while, Sharpe," his companion had whispered. "I have a strong premonition of some impending danger."

"The deuce you have!" remarked Sharpe, who well knew what this meant in a man like Keane, whose psychic faculties were not to be sneered at.

"Yes. I cannot explain it, but there is some hidden danger right ahead of us; of that I am as certain as that we are in the Schwarzwald. We had better lie down a while and await developments quietly."

Nothing loath, Sharpe unfastened his shoulder straps, slid his equipment quietly to the ground, and laid himself down beside his companion.

For the moment all was quiet. The moon was hidden behind a bank of clouds, and it was therefore very dark, but sounds travel far in the night air of the forest, and when they conversed, they spoke only in whispers.

"It may be," remarked Keane, "that the spot we seek is just in front of us, though I cannot see any glade or clearing as yet; it is too dark."

"Is it likely that there are any booby-traps hereabouts, set by this wily professor?" asked his companion.

"I cannot say; he may have some outer system of defence."

"Or even a system of ground signals to announce the approach of strangers, whose presence might be undesirable to him," added Sharpe.

"It is possible," whispered Keane, whose mind was actively engaged in preparation for eventualities, in view of his inexplicable premonitions. Suddenly he started and touched his comrade lightly with his raised forefinger.

"Hist!" he said, in a voice which could not have carried further than a couple of yards Then he carefully raised his head, and, turning his eyes towards the thicket through which they had come, he tried to read the secret which it contained. His alarm was justified, yet was he mystified not a little, for the more immediate danger seemed to come from behind.

"Can you hear it, Sharpe?"

"Yes, the same crackling of twigs; another wild boar," remarked his friend facetiously.

Keane shook his head, for his sensitive ears had told him that the footsteps which he had heard were those of human beings. Nor was he mistaken, for a moment later they both heard distinctly, not merely the crackling of twigs and the rustle of the bracken under heavy footfalls, but voices, human voices, conversing in a guarded and careful manner.

"None of your Schwarzwald peasants this time," he murmured, fingering his Webley already, for he instinctively felt that this time they were beset by danger both before and behind. And indeed, these two men, during all their adventures in the secret service during the war, were never in more deadly peril than at this moment, as they were soon to learn.

Scarcely daring to breathe, much less to whisper now, the two Englishmen watched furtively for the coming of the strangers, who were now less than a score of yards away, but were approaching very stealthily, as though they were searching for something on the ground.

"Who can they be?" wondered Keane. "And what can they be searching for?"

"Poachers," Sharpe was thinking, "merely poachers, searching for their booby-traps."

Nearer and nearer came the dark shadows, and both the airmen had their Webleys trained on them now. In that moment they might have shot them down easily, and before long they would regret they had not done so. But that is not the English way, for the ordinary Englishman would give even a dog his chance, as the saying goes. Still, there are dogs and dogs, and sometimes human dogs are worse than the four-footed ones. But the Englishmen were uncertain; they did not know what world-wide conspirators were these two men. They did not know what fearful deeds would happen even that day on the Hamadian desert, two thousand miles away, but all of it engineered from this spot, and made possible by these two men. And as they did not know, they did not fire, but waited.

"Gott in Himmel, where does that _verdammt_ live wire begin?" asked one of the men in a low but vehement voice. It was the professor himself, searching for one of his own man-traps.

Sharpe glanced at Keane, but the other motioned him not to fire.

"We're learning something, old man!" he whispered. "This is the gateway to the aerodrome."

The two men had passed them now, passed within six yards, and yet had missed them. They were now groping a little way ahead, looking for secret signs and marks lest they should be hoist upon their own petard.

"Donner und Blitzen! Have you found it yet, Fritz?" called the professor a little louder to his friend.

"Here it is, Professor! Be careful ... there are six wires already laid for those _verdammt_ Englishmen, Keane and--what is the name of the other?"

"Sharpe!" rapped out the professor, as though he had known the man all his life.

At these words the two Englishmen looked at each other in blank amazement. And before their astonishment could subside, the opportunity which had been given to them of ridding the world of two great conspirators had passed.

"One--two--six!" they heard the mechanic say, as he helped the professor over the deadly maze, scarcely fifteen yards in front of them, and then their dark forms had merged into the trees and disappeared, their voices becoming fainter and fainter.

"Great Scott!" gasped Sharpe, when he recovered from his astonishment; "we've walked right into the hornets' nest."

"We should have done if we'd gone another fifteen yards," replied Keane, wiping the perspiration from his forehead.

"Fortunate you had that presentiment of impending danger," said his friend.

"We should have been lying dead and half grilled over his deadly wires but for that strange, weird feeling of mine," replied Keane.

"But there, after all our attempts at concealment, he knows all about us."

"Even our names seem familiar to him," remarked the senior airman, greatly puzzled.

"I cannot understand it," replied the other. "Who can have given him this information?"

"Who indeed?" asked Keane. "It is as great a mystery as the other matter."

"Can it be the woodcutter or the clockmaker, do you think, for Hans is sure to have called at Jacob Stendahl's cottage and told him the news."

But Keane shook his head, as he remarked: "Neither Hans nor yet the woodcutter could possibly have told the professor our names. This evil genius must have other sources of information at his command. Possibly he has an agent at Mulhausen aerodrome, or even at Scotland Yard. To a man like this, a thousand ways are open. I cannot say, but this I know, we are on the edge of the biggest mystery I have ever encountered."

"And we might easily have shot him. Bah! it would have been better to have fired, Keane," added Sharpe somewhat bitterly. "Cannot we follow him now?"

"No!" replied his companion, firmly. "It is better as it is."

"Why?" demanded the other.

"Rest content, Sharpe," said Keane. "To-day we have discovered the aerodrome; to-morrow we will capture it."

*CHAPTER XIX*

*THE DEVIL'S WORKSHOP*

Patiently, now, the two Englishmen waited for the dawn. Till then it would not be safe to move in any direction. As they lay in the long bracken and ferns, however, they were able to converse quietly, and to discuss their plans for the coming day. The spot they had come so far to seek was now before them. The live wires, just a few feet ahead of them, had been duly located, and now that the danger was known, it was not insuperable. It was an added mystery to them, nevertheless, how this wizard secured sufficient voltage to make these wires so deadly. They assumed, however, that powerful dynamos, worked by this same silent energy that propelled the aeroplane, were at work somewhere near this spot.

Dawn came at last; a faint yellow streak lit up the horizon away to the east. Then a crimson flush revealed the distant tree-tops, and the moon and stars faded away. A hundred songsters awoke the stillness of the forest, for another day had dawned, and the sable curtain of night rolled westward.

"See, there is a clearing fifty yards ahead," were Keane's first words to his companion.

"It is the aerodrome, the secret aerodrome!" replied Sharpe, peering through the trees.

"Let us work round a little way and find the workshop or hangar. I fancy we shall find it on the other side of the glade."

"Mind those beastly wires, then!" replied Sharpe, as he began to crawl through the dense undergrowth after his companion, who had already started to make a circuit of the outer defences on his hands and knees.

The next half-hour was spent in cautious creeping and crawling just outside those death-dealing wires. At the end of that time, however, Keane made a discovery. He had completed about half the circuit, when, peering carefully through the trees, he fancied he could make out the camouflaged fabric which covered some temporary building. So carefully was this place hidden amongst the trees that he had to look twice or three times before he could make up his mind that he was not mistaken. At last he convinced himself that he had located the workshop, else, why should the place have been so carefully hidden. Waiting for his companion to reach him, he pointed to the object and whispered, "There it is, not thirty yards away!"

"Shall we get over these wires, and rush the place?" asked Sharpe.

"No. Let us continue our journey until we have completed the circuit. We may make another discovery yet. Come along; fortune favours the brave."

They had scarcely crept another hundred yards, however, when a rustling in the leaves, accompanied by a snort, revealed the presence of another wild boar, which had evidently scented their presence.

"Confound the pig!" muttered Sharpe, who was afraid the sounds might lead to their premature discovery. But Keane thought otherwise, for, to his quick mind and instructive genius, this trifling event seemed providential.

"The pig!" he whispered, pointing to the spot whence came the occasional snorts of the angry, disturbed creature.

"What of it?" queried Sharpe.

"Let's get to the other side of the beast and drive it against the wires."

"And roast the brute alive for the benefit of their breakfast, I suppose."

Keane laughed silently, and wondered how far the conspirators used this live wire to keep themselves supplied with food. He knew, however, that a wild boar on the live wires would soon bring out the inmates of that mysterious house in the woods, and would sufficiently distract their attention to give the airmen their opportunity.

The next moment, having made a sufficiently extensive circuit, so as to get the wild boar between them and the wires, they began closing in on the beast, an operation not devoid of peril, should the boar decide to attack them. Fortune favoured them, however. The angry beast, noting the approach of some unseen enemy, by the movements of the tangled undergrowth, half frightened and half infuriated, made off in the direction of the clearing, uttering further snorts. The next moment he had touched the first of those deadly wires, and, with a wild scream which rang through the forest, he leapt into the air, then fell back quivering but dead across that fatal grill.

"Back--back for your life!" hissed Keane, as he made haste back to the spot where they had sheltered, close to the camouflaged hangar.

The next instant the watchers saw the professor and his assistant rush out of the little building, towards the place where the animal lay right across the first four wires. In their excitement they both seemed to have forgotten the presence of the two Englishmen in the woods during the previous evening, for they were both unarmed. Or perhaps it was that they imagined them to be the present victims of their cunning.

"Hoch! Another royal boar for the larder, Fritz!" exclaimed the professor. "We shall have the winter's supply complete very soon."

"Gut, mein herr!" came the answer.

"Better go back and switch off the current, so that we can take it away," urged the chief, and, staying but a second to see the royal victim, the assistant complied.

This was what the two Englishmen had been waiting for. The moment of action had come at last. Gripping their pistols, they made ready to advance and take possession of the hangar during the absence of the inmates.

"Sind Sie fertig, Friedrich?" called the professor.

"Ja, das bin ich!" replied the other, as he left the workshop, and rejoined his companion.

"Come along, the wires are dead now," whispered Keane, and, keeping well within the shadows of the trees, the two men crept forward, gained the rear of the structure, then cautiously worked their way round and entered the hangar unobserved.

One glance about the well-fitted workshop sufficed. There were no further occupants, and they lowered their pistols. Sharpe at once sprang to the lever which regulated the powerful electrical current and clutched it. In another instant the two men without would have paid the extreme penalty, for they would have been instantly killed by their own evil device, but Keane stopped him:--

"Don't!" he said. "We have much to learn. The professor at least must be taken alive, if possible. The secret he holds is too precious to be lost. Let us hide!"

"Where can we hide?" asked the other, somewhat disappointed, and amazed at the further risks which his companion appeared willing to take in order to gratify an insatiable curiosity. "The tables may be quickly turned upon us."

"We can shoot them as a last resort, if that is necessary," urged Keane, who knew the priceless value of the secrets which this place contained.

"Hist! They are coming."

"This way!" whispered Keane, and he drew his companion into a little recess, which had evidently been curtained off for the mechanic's sleeping berth.

They had barely withdrawn themselves into this narrow apartment when the two men entered, dragging the carcase of the wild boar with them.

"Leave it there for a moment, Strauss. The message from the Rittmeister is due. I must also send him that other message again, as the first has not been acknowledged," were the professor's first words.

"Yes, sir. Shall I start the dynamos again?" asked the assistant.

"Perhaps you'd better, but first hand me that message book and the secret code."

The next moment the professor was busy at the wireless keys, transmitting some message to the far deserts of Arabia.

"By all the saints," gasped Keane, "he's sending a message to the raider, the _Scorpion_, as he calls it. I must have that secret code at all hazards. I wonder what he is saying?"

For some time the chief conspirator was engaged coding and decoding messages at the little table where the aerials, carefully hidden amongst the trees without, had their terminus. And in that moment Keane thanked his stars that he had waited for this, for he saw new possibilities opening out before him. Once in possession of this mechanism and the necessary codes, he could communicate at will with the distant raider, who was threatening the whole civilised world by his almost superhuman powers of brigandage. He could recall the raider also, and make his capture certain, once he could secure absolute possession of this little citadel.

For the present he could do nothing but wait, however, and see how matters developed. Once, the assistant came quite close to their hiding-place, and both men again gripped their Webleys. At this moment even to breathe seemed fraught with danger. If the man should enter the little apartment, he must die, and the professor must be immediately threatened with the same penalty unless he surrendered.

"Ha! So far so good!" gasped Keane, as the mechanic recrossed the workshop without actually entering their hiding-place.

"Teufel!" spluttered the professor. "Here is that fool Tempest trying to communicate with those two _verdammt_ Englishmen who are still roaming about in the Schwarzwald. He little knows that we possess his secret code."

"Himmel! What does he say?" asked the other.

"Wants them to report progress at once, and let him know how matters stand," said Weissmann in a mocking tone. "He says he will come over himself, if necessary."

"Donnerwetter! Ask him to come, Professor. He might as well grill with his accomplices on the live wires, for that's where they'll be before the day is out, unless they abandon their futile search," replied Strauss.

"This fiend is a perfect wizard!" thought Keane, and his glance signified as much to Sharpe. "How he manages to get hold of these secrets is beyond me. And yet, there is a defect in his mad science, for he does not know that we're here, and that his own life is in our hands. Fool that he is, he will soon learn that the wit of an Englishman is more than a match for his boasted knowledge," and here the senior airman carefully withdrew a cartridge from his Webley and inserted another, silently--a cartridge that had a specific mission. His companion watched him and repeated the action with his own weapon, for he understood.

"Blitz! but I've half a mind to send for Tempest," mused the professor, who was still toying with the keys of the wireless instrument.

"Send for him, Professor," urged his accomplice. "Those Englishmen are getting too close to be pleasant. The British army of occupation will be carrying out a thorough search of the Schwarzwald if these men get away, and then where shall we be?"

"We are in the neutral zone, though," replied the other.

"But we're contravening the Peace Regulations, sir, and the English will not stand upon ceremony. It will be too late should these men get away."

"Donner und Teufel!" rasped out the angry professor. "Don't speak to me of the Peace Regulations. There will be no peace till Germany regains all and more than all she has lost. I will send for this Commissioner of Aerial Police, for I believe that he and his two accomplices, Keane and Sharpe, are the only ones so far who know anything that matters about the secret of the Schwarzwald," and he began to tap the keys, reeling out the words as he sent them.

Keane listened acutely for the cyphers of the code. They were:--

"Z--X--B--T--V--O--P..."

and he understood that Tempest was to come at once, make for Mulhausen aerodrome, then take a bee-line, east-north-east over the Schwarzwald until he saw a smoke column, where a suitable landing-ground would be found, and his accomplices would await him.

"Ach!" shrieked the professor, with a fiendish laugh. "The smoke column will mark his last resting-place. They shall all be buried together, these mad Englishmen. We will have more live wires stretched across his landing-ground, and as the wild boar died, so will these men die who dared to follow me into the Schwarzwald."

"The wild boar! Hoch! Hoch!" exclaimed his companion. "It is a fitting tribute for the English are swine!"

"And the _Scorpion_ shall witness the inglorious end of these men," cried the professor, as a sudden idea came into his mind.

"Der _Scorpion_?" queried Fritz, looking up amazed from his task. "What do you mean, Professor?"

"Why, the Rittmeister will have finished his work in the Hamadian Desert this afternoon. His instructions are to resign the Sultanate of those regions for the present, for the skies will be thick with British scouts by to-morrow."

"But then he goes to Ireland to work with the revolutionists there, does he not, mein herr?"

"Ja! ja! but I will ask him to call here for a day or two before he proceeds. He will have much to tell us, and Spitzer, Carl and Max would like to see these dangerous opponents safely out of the way, for at present they are the only enemies to be considered."

"Gut!" ejaculated Strauss, catching something of the professor's enthusiasm.

Keane would have intervened before this, for he had noted Sharpe's impatience, but he intimated as well as he could by mute signs and otherwise, that the fiend was doing their work for them.

"Let him send this message first," he whispered in his companion's ears, "and then----" But the sentence was completed by further cabalistic signs.

Again the professor turned to the keys, and sent his last instructions through the ether waves to his confederate, the brigand of the eastern skies.

*CHAPTER XX*

*"HANDS UP!"*

"Haende in die hohe!" cried Keane as soon as the last message had been sent.

"Der Teufel!" gasped the professor as two swift shadows darted out from behind the curtain, and the two men whom he had just been discussing with such utter contempt confronted him and his accomplice with gleaming pistols.

"Hands up!" repeated Keane, anxious to give the professor another chance.

With a blasphemous oath the man of evil genius, who saw that he had been outwitted, reached for a small hand grenade which lay beside him on the table, and shouted:--

"Never!"

"Then take that!" cried the Englishman, and two puffs of greenish smoke, following a sharp crackle, burst simultaneously from the pistols, for they had both fired together.

The new Asphixor bullets took immediate effect. Both the Germans staggered, clutched their throats as though to ward off the effects of this new powerful gas recently discovered and adapted by that eminent British scientist, Sir Joseph Verne--then lurched and fell, whilst their opponents stepped back and quickly fitted on their safety masks.

"They are both sound asleep," observed Keane, when, the fumes having cleared away, he threw aside his respirator and carefully examined the unconscious men.

"Let them sleep," said Sharpe, who would have adopted even more drastic measures if he could have had his own way. "'Tis scant mercy they would have shown to us if we had been in their power."

"And now let us get to work, for they will awaken in seven or eight hours, and we have much to do. We must prepare for Colonel Tempest, and also for this raider," urged Keane.

"But they will not come to-day, Captain."

"Scarcely, but we must be prepared for anything. There are only a couple of us."

"Shall we secure these men, in case they awake earlier than the stipulated time?"

"No, let us remove their slumbering forms behind the curtain there; we will attend to them before they awake. I do not like the idea of strapping down unconscious men, even though they are criminals. We will watch them from time to time."

Then for the next half-hour they carried out a careful examination of the hangar and its contents. They were amazed at the intricate and wonderful mechanism with which the place was fitted. It seemed impossible that these things could have been transported hither without attracting attention. Parts of aeroplane wings, struts, propellers, engine-fittings, strange, weird-looking cylinders, retorts, analytical appliances, instruments and vessels for chemical research, powerful but silent dynamos, and numberless other things, all neatly arranged, and apparently in working order, half filled the place.

The further they carried their investigation the more were these two Englishmen bewildered by what they saw.

"Is it possible," gasped Keane, "or am I only dreaming? We have discovered the home of the super-alchemist. After this, nothing will surprise me."

"We have discovered the devil's workshop," replied Sharpe, who did not appear to be half so enraptured as his friend.

"Nay, we shall find the philosopher's stone, or the _elixir vitae_ soon," replied Keane, continuing his investigation.

"We are more likely to find the _elixir mortis_ than anything else," said the gloomy one. "This place gives me the shivers. I am sure that I shall have cold feet for the rest of my life."

"After this, Hermes and Geber will be dull reading," continued the enthusiast. "Give me the Schwarzwald every time for the real thrill of the alchemist."

"Their time might have been more profitably employed, at any rate," remarked Sharpe.

"Yes, it is a thousand pities that the wonderful brain which designed and organised all this should have had nothing better in view than brigandage and world revolution."

"More misdirected energy," moaned Sharpe; "the greatest brains often make the greatest criminals."

"You're a veritable misanthrope, Sharpe!" said his companion, laughing.

"I have reason to be," returned the other.

"What do you mean?"

"I mean this--we're not out of the wood yet."

"I agree; we're in the very centre of it," replied Keane.

"Yet you did not inflict the _coup de grace_ on the diabolical vipers, and they will shortly awake. Moreover, the _Scorpion_ may arrive unexpectedly, and we shall be unprepared for her."

"What would you do?"

"Bring over the machines from Mulhausen, ready to fight this air fiend when he comes."

"Ho! So you're longing for another real air fight, are you, like the 'scraps' we used to have with the Richthofen 'circus'?"

"At any rate, we'd better prepare. Then I'd bind those two criminals hand and foot or surround them with live wires, so that, should they awake unexpectedly, they would not dare to stir."

"There is certainly something in what you suggest about bringing the aeroplanes over, though we should have a deuce of a job to land them in this place; they're by no means possessed of the powers of a helicopter. However, I'll get into touch with Colonel Tempest and ask for immediate assistance, and also ask him to bring over Professor Verne to investigate these mysterious engineering and chemical appliances."

So, leaving the workshop, the live wires and the prisoners to the care of Sharpe, the senior airman devoted all the rest of that morning to investigating the wireless apparatus, examining the secret codes, and trying to get into touch with the Commissioner of Aerial Police. In this, however, he was not very successful, for the air was full of messages, concerning an overdue air-liner which had been expected for some time at Cairo. Perhaps his message had been jammed or lost in the aerial jostle.

Colonel Tempest was almost at his wits' end. He sorely needed the help of his able assistants. He wanted to send them out east to chase this daring brigand off the trade routes.

He was unable also to comply with the request for assistance, when at length it did reach him, for all his best fighting men, with the exception of these two in the Black Forest, had been sent after the raider. He promised, however, to come personally at the earliest possible moment, as soon as matters had been cleared up a little.

Again and again Keane tried to reach him with brief, but urgent coded messages, for he was now getting extremely anxious lest the raider should appear before they were ready. Sharpe, however, who was eminently practical, had taken the professor's own tip, and had laid wires across the glade, which, when properly connected up, would make it a dangerous proceeding for a hostile aeroplane to land there, while, in the event of a friendly one appearing, the current could be immediately switched off. He had seen to the prisoners as well, for, unknown to Keane, he had, on the first signs of awakening, given to each of them a sufficiently strong soporific to extend the period of their quiescence for a considerably longer period, so that, late that afternoon, his friend was somewhat alarmed at their quietude.

That night they watched in turns, and relieved each other every two hours. When morning came they climbed the highest trees and scanned the horizon in every direction for the promised help, and also for the _Scorpion_. But although the column of smoke from the fire which had been lighted, ascended all day in one long grey streak to guide the British airmen, yet morning wore on to afternoon, and no assistance came.

Keane sent message after message, but apparently to no purpose. The very heavens were full of messages, for the whole civilized world had been roused by the last daring feat of the phantom airman. London, Paris, Cairo, Delhi and New York were clamouring for his immediate capture and execution. Strong things, too, were being said about the incapacity of the much vaunted aerial police, but all the world realised that the task before these men was almost superhuman.

Twice an urgent message came recalling the two Englishmen, but Keane replied with the one word, "Impossible!"

And all this time the raider, who was carefully hiding for a few days, delighted his companions by retailing with much gusto such of these messages as he had been able to piece together from the aerial jumble.

"Let them send all their available machines and pilots out east," he had said to Carl and Max, "then we will quietly slip across Europe to Ireland, where everything is ripe for the promised revolution."

"And the Schwarzwald?" queried Max.

"Oh, we will call there for a few hours en route," replied the pirate, calmly relighting his pipe, "The professor will understand our silence and inactivity."

So the third morning came, and Keane, whose anxiety regarding the still sleeping prisoners had been allayed by Sharpe, who smilingly confessed what he had done, now became fearfully uneasy as to the condition of affairs.

"For heaven's sake light that beacon again!" he ordered. "If assistance does not arrive to-day, all these secrets I have endeavoured to rescue will be lost."

"What will you do?" asked his companion, who was already applying a match to the pile of dried tinder and sticks.

"Blow the whole place up," he replied.

"And shoot the prisoners?" ventured his friend, slyly.

"No."

"What then?"

"Rouse them up, somehow, handcuff them together and take them away."

"Some job that," remarked Sharpe, looking up at the long thin trail of smoke, for there was still an absence of wind currents.

Even as he gazed into the sky, however, he caught sight of a tiny speck hovering at twelve thousand feet, and he almost shouted, "Aeroplane!"

"Where?" asked his startled comrade, whose nerves had undergone some strain during the past few days.

"Right up in the blue. There, can you see her?"

"Yes, I have her now, but she's very high. Can it be the _Scorpion_, do you think?" asked the senior.

"Cannot say yet. I'll fetch the glasses."

"Run for them, quickly! I cannot hear her engines at all. It must be the brigand."

"Ah, there, I hear the engines now, very faintly, though. Rolls-Royce engines too, thank God!" exclaimed Keane fervently, as he recognised the well-known sound, and knew that assistance had arrived at last, in the shape of at least one Bristol Fighter.

"It's all right, Sharpe. Cut off that beastly current. Tempest will be here in a minute."

"Are you sure it's Tempest?"

"Yes. Listen to that! Now he's cut his engine out again, and he's coming down. It's the chief right enough; I should know his flying amongst a score of aeroplanes."

The wires were cut off, a temporary landing-tee quickly rigged up on the ground, and frantic signals were made to the pilot, who was now rapidly coming down in sharp spirals.

A few minutes later the intrepid pilot flattened out above the tree tops, dipped again, banked steeply, and sideslipped almost to the ground, in order to get into the confined and narrow space which served the _Scorpion_ for an aerodrome. Scarcely had he landed when another machine, which had followed him from England, performed the same highly-skilled manoeuvre, and taxied up to the little group.

*CHAPTER XXI*

*THE COMING FIGHT*

"Good-morning, Colonel!" cried the two airmen, saluting their chief smartly, as he still sat in the aeroplane, looking not a little crabbed and sour, as he secretly swore at the infamous stretch of ground misnamed an aerodrome; then turned his gaze upon the two airmen who had appealed for assistance.

"Morning! So this is where you young cubs spend your holidays, while the whole world is ramping at me for not catching this infernal brigand. What have you got to say for yourselves?"

Keane was not at all put out by this dour greeting; he knew his chief too well, and admired him accordingly. Merit is not always accompanied by a bland and urbane countenance, neither do brains always accompany a white shirt front.

"I have that to say which will almost make you jump out of your skin, sir," replied Keane, "but we must somehow get these aeroplanes under cover, or properly camouflaged, for the _Scorpion_ may arrive any minute."

"Eh? What's that you say, boy?" exclaimed Tempest, leaping from the fuselage. "The _Scorpion_?"

"Yes, sir."

"Why, that is the name of your infernal raider, isn't it, Captain Watson?" and here the colonel turned and addressed his passenger, who was none other than the skipper of the air-liner which had been so roughly handled in the Hamadian Desert.

"The same, sir."

"And the professor, Keane? I sent you to track the professor. Have you found him?"

"He is our prisoner, Colonel," and Keane bowed stiffly, and pointed to the half-hidden hangar, where the two prisoners, who were now partly roused, had been safely secured.

An exclamation of pleasure and surprise broke from this dour-looking man when he heard this news, and his face became wreathed with smiles as he advanced to both Keane and Sharpe, shook them warmly by the hand, and said:--

"Thank you, my boys; I knew if it could be done you would do it, though I could ill spare you for the job. Yesterday my reputation was in shreds; I am to be charged with inefficiency, and a public enquiry is to be held. But you two wolf cubs have re-established my character; I can never thank you enough. Now lead on, show us this evil-minded genius! Professor Verne here, who has come in the second Bristol, with Captain Hooper, is anxious to see him. He may redeem him yet from the error of his ways, and it is vital that this secret of his should be in other and better hands, else it will always be a danger to the public."

So, whilst the party were conducted indoors, and shown the marvels of the modern house of alchemy, the two professors were introduced, and began a series of disputations, very embittered at first, as the German, though relieved of his bonds, and made as comfortable as the circumstances would permit, resolutely refused to give any particulars of his discovery, or even to display the slightest amiability towards his distinguished visitor, though they were not unknown to each other, and had even studied at Heidelberg together in their younger days.

Meanwhile, all possible steps were taken to prepare for the possible arrival of the _Scorpion_. The Bristol machines, after being carefully stowed away in a gap between the trees, were so camouflaged by branches of pine and larch that they presented but a very indistinct object from the air, and, unless their presence were known, might easily remain unobserved.

After some time had been spent in examining the highly developed and intricate mechanism of the devil's workshop, as the place was now called, the Commissioner suddenly turned upon his chief mentor, and said:--

"By the way, Keane, have you discovered any drawings or designs of this wonderful aeroplane? I don't see any amongst this pile of papers, and the professor does not seem inclined to help us at all."

"No, sir. We have searched the place carefully, but we have found nothing. Part of the machine could certainly be reconstructed from those spares, but all the important parts are missing. I have an overwhelming curiosity to see the machine, though, and hope that I may not have this pleasure much longer delayed."

"Then we have nothing but these photographs," returned the captain.

"Photographs?" echoed Keane.

"Yes. Why, I forgot to tell you in the bewilderment and excitement of the last hour, that Captain Watson here managed to secure three snapshots of the raider in mid-air, whilst his airship was being attacked."

"It was the boy Gadget who secured them, sir," interposed the air-skipper, anxious to give credit where credit was due.

"Oh, yes, Keane, I ought to say that it was a smart little beggar called Gadget, a stowaway, who really secured the photographs, and hid them away from the brigand. We must see that the little chap is properly rewarded when we return."

"Let me see the pictures, sir," requested Keane, eager to get some idea of his future opponent.

"Here they are. I have had them developed and enlarged. They should be extremely useful to us, as we shall shortly have to encounter this Sultan Selim, Air King of the Hamadian Desert, the world's greatest bandit, who had the audacity to send me this document by the captain."

And here the colonel, having retailed the whole story of the fight in the desert, showed the brigand's letter, which had been brought to London the previous day by the fast aeroplane which had carried the skipper of the air-liner.

Keane turned in amazement from the clear photographs of the phantom-bird to the brief, audacious letter of the phantom airman, and read as follows:--

"To Colonel Tempest, D.S.O., M.C.,

Commissioner of Aerial Police, Scotland Yard, London, W.C.

"Greetings from Sultan Selim, Air King of the Hamadian Desert. I regret to inform you that of late there has been a serious increase of aerial crime in these regions. The frequent passing of large airships containing mails and other commodities, without due payment of tribute to my customs officials, is a serious infringement of the laws of my dominion. This action not only imperils the liberties of small communities, but is also a crafty form of aerial brigandage, inasmuch as it defrauds my exchequer of its just and equitable revenue. This practice must cease forthwith, and I have taken steps to-day which, in my opinion, will render it unwise for this shameful trespass to continue. The bearer of this letter will give you further details of the action which I have been compelled to take on behalf of my subjects. Your five missing scouts will be found between the wells of Nefud and the Hedjaz coast. I have destroyed their machines as a salutary warning to future violaters of these my dominions."

Keane could scarcely restrain a smile when he laid down this wily, half-humorous, half-threatening epistolary from the aerial pirate.

"What do you think of it?" asked the colonel.

"It's a topping letter, sir, but I think he's trying hard to be funny, this von Spitzer, as you call him. A German with a sense of humour, sir, that's the best way to regard him," replied the airman.

"Humour indeed!" rasped out the colonel, becoming ruffled. "It's confounded impudence, and worse, when you remember that, apart from the damage to the airship, which is considerable, there is a net loss of specie and other valuables--to wit, the Maharajah's jewels--which is estimated at a quarter of a million sterling. I only hope and pray that we may encounter and waylay this bandit before he does any more damage. The deuce only knows what he'll do next, or where he'll go."

"Ireland is to be the scene of his next adventure, sir," remarked Keane.

"Ireland?"

"Yes, sir."

"Are you sure?"

"I heard the professor say so. They are to work hand in hand with the revolutionists there, and stir up strife which will make that unhappy land a still greater thorn in the side of Great Britain."

"Just what I feared!" exclaimed the now irate commissioner. "That explains partly those mysterious messages and rumours floating about Dingle Bay, and unfortunately I have had to withdraw nearly all the aerial police from that quarter to send them out east."

"You might as well recall them, sir."

"Why?"

"The raider has left the Hamadian Desert by this time, and is in hiding somewhere, but will call here on his way to Ireland."

"H'm! We're being thoroughly fooled, and if you hadn't found this demon's nest I should have gone mad. At any rate I should have been compelled to resign my post."

"Still, public opinion had to be satisfied, and you sent the patrols where the public demanded that they should be sent. Besides, if you recall them now, this raider will probably pick up your messages and change his tactics. I can tell you this, Colonel, that while he can get his necessary supplies of uranis, and a few extra spares from the workshop here, this von Spitzer intends to carry out his mad policy of destroying the civilized world by piecemeal. It is all part of a great plan to save Germany from the evil consequences of the Peace terms. But, whilst we hold this citadel, and retain these two men captive, his activities are limited to his present supply of this secret element--uranis."

The colonel swore under his breath, and went to examine the prisoners, to make sure that there was no chance of their escaping, for he felt the truth of Keane's words. He now felt grateful that the airman had not responded to the message for his recall, although it had amounted to a serious breach of discipline.

"Ah, well," he said at length, "it only remains to capture this raider, and the whole system of their clever and daring attempt to convulse the Allies, break up their international system of mail transit, stop the intercourse of civilized nations, and cause a world revolution--all these things will fail."

So their efforts were redoubled to make preparations to capture the wonder 'plane, should it descend on the aerodrome. A couple of machine guns were found, and mounted, under the charge of Sharpe and Captain Hooper, though the skipper of the airliner pointed out that the _Scorpion_ carried bullet-proof armour.

"You will need to hit her in a vital spot," he said, "so that your first burst may be your last, or she will be up again like a helicopter."

"Then we must have the two Bristols ready," urged the colonel, "though it's a deuce of a hole to get out of with this new type of a Bristol Fighter."

"And the petrol, sir?" asked Keane, who, was rather anxious on this point, for he hoped that the _Scorpion_ would become his victim in the coming air fight.

"There may be sufficient for another two hours, certainly not more."

"That means unless the _Scorpion_ chooses to stay and fight, she'll simply leave us."

"Von Spitzer will fight unless I stop him!" called out the professor from behind the curtains, where he was confined under the charge of his colleague of other days, for he had been listening to the conversation.

"So much the better!" replied Keane, tartly.

"And when the fight is over there won't be many of you left alive to tell the story," came the rejoinder.

*CHAPTER XXII*

*AN AERIAL DUEL*

"Message from the _Scorpion_, sir!" cried Keane, a little before midday, from the little key-board where he had been patiently waiting for the last hour.

"Good! What does the brigand say?" asked Tempest.

"Expects to be here within an hour."

"Then we haven't a moment to lose," replied the colonel. "At the same time, I am glad we have had this message, for to be forewarned is to be fore-armed."

Then, turning to Keane, whom he knew to be his best and most brilliant pilot, he said, "Where would you like to be stationed, boy?"

A sudden gleam came into the youth's eyes, for he saw that his chance had come.

"Let me have all the spare petrol from the other machine, and let me get up above the clouds in that new No. 7 Bristol Fighter which you brought over, sir."

"I'm afraid it means certain death for you, my lad," replied the chief, after a pause, unwilling to permit the youth to take such unknown risks, and yet still more unwilling to deny him his request. "This _Scorpion_, according to Captain Watson, must be some stunting machine."

"I am willing to take the risks, sir," replied Keane. "It is not my first fight with a Hun."

"Don't I know it, boy!" replied the other, gazing with fond admiration into the frank and pleasing face of the pilot. "The ribbons which you gained speak for themselves, but they don't tell half the story. Don't I remember the morning when you went over the line by yourself, and encountered seven enemy machines, how you fought with them for an hour and brought five of them down, chased the others till your machine threatened to break up, then turned and staggered home with your wings shot to ribbons?" and the colonel fondly patted the youth's shoulder.

"Then let me go, sir. The brigand will be not a little confounded to find himself attacked both from the ground and the air at the same time."

"You shall go!" said the colonel after another pause. "Will you take a gunner with you?"

"No, sir. I would rather go alone."

And while the petrol was drawn off from the other machine, No. 7 was brought out, filled up, and tested, ready to start at a moment's notice. The Vickers gun, fixed forward to fire through the propeller, was carefully examined, and several drums of the new armour-piercing bullets placed in position. Another moment was given to the alignment of the gun-sight, a matter of supreme importance in an aerial duel like this one promised to be, for the slightest error in this respect would be like courting disaster.

Ten minutes later the signal was given to stand clear, the colonel himself swung the propeller, and, instantly, the powerful 350 H.P. Rolls-Royce burst into life with a crackle and a roar, and, when the chocks were withdrawn, the Bristol dashed across the ground, leapt into the air at sixty yards, and by a steep climb just cleared the tops of the trees on the edge of the forest.

"What are his chances, Colonel?" asked Captain Hooper.

The chief shook his head as though doubtful of the result, then, after watching the machine for a moment, as it climbed in rapid spirals up into the clouds which half covered the sky at four thousand feet, he said:--

"There is no pilot aboard the _Scorpion_, or any other machine for that matter, who can hold a candle to Keane, but--it is the amazing speed and climbing powers of the other machine that I fear. Still, it will be some fight, and if we fail to trap the brigand down here, well, it is just possible, despite his disadvantages, that Keane may bring the rascal down. He'll have to keep well out of sight, though, and run at less than half-throttle behind that cloud bank till the moment comes to strike. And now to stations, all of you, and keep well out of sight. Professor Verne, I am afraid you will have to take charge of the two prisoners. Don't let them get away for heaven's sake. You must shoot them first."

"I'll take care of them, Colonel," replied the eminent man, "though it is a somewhat unusual occupation for me."

"Needs must when the devil drives, Professor! I told you it would be some desperate adventure. Have you had any luck with that evil genius, yet?"

"Not the slightest, so far. He is prejudiced against the English mind, and is secretly rejoicing over the expected arrival of the _Scorpion_."

"Tell him from me, Professor, that if he attempts to escape, I shall shoot both him and his accomplice without the slightest compunction," said the colonel, as he turned away to re-examine all his defensive posts, and to alter the position of one of the machine guns, which had been entrusted to Captain Sharpe.

Fifteen minutes passed away, and the Bristol, hidden away behind the cloud bank, kept its engine well-throttled down, lest the roar of the powerful motor should reveal its presence, when, suddenly, from one of the watchers, the cry arose:--

"Aeroplane approaching from the south-east."

"Is it the _Scorpion_, Captain Watson?" the colonel asked, as soon as the machine had been located.

"Yes, it is the same brigand, sir."

Then, with amazement bordering on the supernatural, the little garrison saw the _Scorpion_ moving across the sky at a miraculous speed, and making directly for the secret aerodrome. Once or twice it circled around at three thousand feet, then dived a clean two thousand five hundred upon its objective, silently, like a mysterious phantom bird. At five hundred feet it flattened out, rode gaily above the tree tops, then swooping like a falcon, once more touched the ground lightly, and came to rest within thirty yards of the secret hangar.

"Haende in die hohe!" cried Colonel Tempest, stepping out into the open, and confronting the visitors with a couple of revolvers, as they prepared to leap from the armoured conning-tower.

"Ach Himmel! We are betrayed!" cried Spitzer. "The _verdammt_ English have captured the aerodrome."

Without thought of surrender the brigands tumbled swiftly back into the armoured cell, just as a shower of bullets from both revolvers swept the upper surface of the cockpit.

"Fire!" shouted Tempest, stepping back, as the daring bandits, regardless of the danger, started the propellers once more by means of the self-starting knob, within the conning-tower.