"That, it was impossible to find out during our short stay over there," replied Keane, "but I discovered from someone who had been in close touch with him just about the time peace was signed, that he had expressed himself in very hopeful terms."

"Was he a very communicative type of man, then, did you learn?"

"No; on the contrary, he seldom spoke of his work, but on this occasion, when he communicated this information, he was very much annoyed at the defeat of Germany, and considered that his country had been betrayed into a hasty peace."

"And what happened to him after that?" asked the colonel.

"Shortly afterwards he disappeared completely, taking with him all the apparatus connected with his research work, also a highly skilled mechanic who had been specially trained by him for a number of years. But he left not a trace of himself or his work," said the captain, pausing for a moment to light a cigarette.

"Do you think he is acting under any instructions from his authorities?"

"No, certainly not; he distrusts his present Government entirely, and considers them traitors to the Fatherland."

There was another brief silence, whilst the three men, wrapt in deep thought, sat looking into the fire, or watched the rings of tobacco smoke curling upwards to the ceiling. At last, Captain Sharpe observed:–

"A powerful intellect like that did not suddenly disappear in this way without some ulterior motive, Colonel Tempest."

"Obviously not," returned the latter briefly, for he was deep in contemplation, and his mind was searching for some clue. At length he turned to the senior captain and said:–

"This silent engine theory, Keane, what do you think of it?"

Keane shook his head doubtfully, and the colonel handed to him once more the recent wireless message from Delhi, adding merely:–

"Do you think it possible?"

"Scarcely," replied Keane carefully, "but with a master mind like this, one never knows. It will be necessary for you to consult the most eminent professors of science and chemistry at once."

"I intend to visit Professor Verne at his house first thing to-morrow, or rather to-day, for it is already morning."

"But the aeroplane," added Sharpe, who had been perusing the Delhi message, "this also must have been specially built for this new gas."

"Given the one, the other would naturally follow, and would be the lesser task of the two, for this man is a great engineer as well," said Keane.

"It is a deep well of mystery," continued Tempest after another pause; "but something must be done at once. To-morrow the morning papers will be full of it. Next day Parliament meets, and questions will be asked, and it will all come upon us. I shall have to meet the Home Secretary as soon as I have interviewed Professor Verne, and Lord Hamilton will not be easily satisfied. The public will also be clamouring for information on the subject, and they will have to be appeased and calmed. The Stock Exchange will begin to talk also, and to demand compensation for the companies whose properties have been damaged. Insurance rates, marine and otherwise, will be raised, and Lloyd's underwriters will not fail to make a fuss. Now, gentlemen, what steps can we take to deal with these raiders in the immediate future?"

Send us after this mystery 'plane on fast scouts with plenty of machine-gun ammunition," urged Sharpe.

"I cannot spare you for that, but I have already ordered strong patrols of aerial police to search for the brigands. I must have you here or somewhere within call. At any rate, I cannot let you go further than Germany. It may be necessary to send you there again."

"On what account, sir?" asked Keane.

"To find the aerodrome which this raider calls 'home,' for he must have a rendezvous somewhere if only to obtain supplies and repairs."

"And that secret aerodrome must be somewhere in Germany, hidden away in some out-of-the-way place," ventured Sharpe.

"But in what part of Germany?" asked the commissioner.

"Let me see," cried Keane, rising to his feet, and walking across the room to where the large map of Germany hung upon the wall–"why, it must be in the Schwarzwald!"

"The Schwarzwald!" exclaimed the other two.

"Yes, it is by far the best hiding-place in the whole country. One may tramp for days and never see a soul. It must be somewhere in the Schwarzwald."

"Then to the Schwarzwald you must go to-morrow, adopting whatever disguises you desire, and you must find this hidden spot where the conspiracy has been hatched," concluded the colonel.

CHAPTER V
THE AERIAL LINER

The airship liner, Empress of India, was preparing to leave her moorings, just outside the ancient city of Delhi, for Cairo and London. This mammoth airship was one of the finest vessels which sailed regularly from London, east and west, girdling the world, and linking up the British Empire along the All-Red Route. She had few passengers, as she carried an unusually heavy cargo of mails for Egypt and England, and a considerable amount of specie for the Bank of England. Several persons of note, however, figured amongst her saloon passengers, including the Maharajah of Bangapore, an Anglo-Indian judge, and a retired colonel of the Indian army.

She was timed to depart at mid-day, and during the morning mailplanes had been arriving from every part of India with their cargoes of mail-bags, already sorted for the western trip.

The great mammoth now rode easily with the wind, moored by three stout cables to the great tower which rose above the roof gardens of the air-station. An electric lift conveyed the passengers and mails to the summit of this lofty tower, from whence a covered-in gangway led to the long corridors which lined the interior of the rigid airship.

"Have all the engines been tested?" the captain asks of the chief engineer, as he comes aboard with his navigating officer.

"Yes, sir."

"All the passengers aboard?" he asks next of the ground officer.

"All except the maharajah, Captain, and I expect him any moment."

"Excellent," replied the skipper. "There's a good deal of bullion aboard from the Indian banks, I hear, and the rajah himself is likely touring a lot of valuables with him, I understand, as he is to attend several court functions at St. James's Palace."

"Yes, sir. I hope you won't meet that aerial raider," replied the ground officer.

"Poof! What can he do? He can't board us in mid-air! Besides, I hear that the aerial police are on his track, and that all their fast scouts are patrolling the mail routes."

"Yes, you'll have an aerial escort with you for the first two hundred miles, Captain. They'll pick you up shortly after you leave here."

"Absolutely a waste of time. The police could be much better employed in searching for these rascals."

"Well, perhaps you're right," replied the ground official. "They certainly cannot board you in mid-air, as you observe, and they cannot set you on fire as they did the early Zeppelins, for helium won't burn."

This conversation was interrupted by shouts and cheers which reached the speakers from down below.

"Hullo! here comes the rajah. I must go down and welcome him," said the captain, as a fanfare of trumpets announced the arrival of the great Indian chief.

Then, with all the ceremonial and pomp of the East, the Maharajah of Bangapore was welcomed aboard the luxurious air-liner, and, accompanied by his personal attendants, he was shown with much obsequiousness to his private saloon. His baggage, containing treasures worth a king's ransom, was likewise transferred, under the supervision of his chamberlain, from the ground to his suite of apartments.

The clock in the palace of the Great Mogul in the old city of Delhi strikes twelve, and the captain's voice is heard once more, as he speaks from the rear gondola:–

"All ready?"

"Yes, sir, all clear!"

A button is pressed and the water ballast tanks discharge their cargo to lighten the ship, and then swiftly comes the final order:–

"Let go!"

And as the cables are slipped from the mooring tower, the light gangway is drawn back, the crowd down below cheer, and the giant airship backs out, carried by the force of the wind alone till she is well clear of the station. Then her engines open up gradually. She turns until her nose points almost due west, then slips away on her four thousand miles' journey over many a classic land, desert, forest and sea towards the centre of the world's greatest empire.

About four o'clock that afternoon, as Judge Jefferson sat and talked with his friend Colonel Wilson in one of the rear gondolas where smoking was permitted, he remarked that this was his seventh trip home to England by the aerial route, and declared that he could well spend the rest of his lifetime in such a pleasant mode of travel.

"There's no fatigue whatever," he added; "nothing of the jolt and jar which you get in the railway carriage. As for the journey by sea, I was so ill during my last voyage that I simply couldn't face the sea again. A storm at sea is of all things the most uncomfortable. If we meet with a storm on the air-route we can either go above it or pass on one side, as most storms are only local affairs."

"Not to speak of the time that is wasted by land or sea-travel," added the colonel.

"Exactly," replied the judge.

"Only to think that in forty-eight hours we shall be in London, even allowing for a two hours' stay in Cairo to pick up further mails and passengers."

"Wonderful! Wonderful!" agreed his companion.

"And the absence of heat is some consideration, when travelling in a land like India," continued the colonel as he flicked off the end of his cigar.

"Yes. The stifling heat, particularly in May, June and July, when you get the hot dry winds, is altogether insufferable in those stuffy railway carriages, while up here it is delightfully cool and bracing, and the view is magnificent."

"Hullo! what is that fine river down there?" asked the judge, as he looked down through the clear, tropical atmosphere on to the delightful landscape of river, plain and forest three thousand feet below.

"Oh, that must be the Indus, the King River of Vedic poetry, a wonderful stream, two thousand miles in length," said the colonel, consulting his pocket map.

"Can it really be the Indus?"

"It is indeed."

"Then we have already travelled four hundred miles since noon across the burning plains of India, and we have reached the confines of this wonderful land," replied Jefferson.

"Yes, we have indeed. We shall soon enter the native state of Baluchistan. See yonder, right ahead of us, I can already make out the highest peaks of the Sulaiman Mountains. We are already rising to cross them."

"And this evening we shall cross the troubled territory of Afghanistan."

"Yes," replied the colonel, "and by midnight, if all goes well, we shall be sailing over Persia."

"Persia, the land of enchantment," mused the judge.

"And of the Arabian Nights, those wonderful tales which charmed our boyhood–the land of Aladdin, of the wonderful lamp, and the magic carpet."

"The magic carpet," laughed the judge. "This is the real magic carpet. The author of that wonderful story never dreamt that the day would really come when the traveller from other lands, reclining in luxury, would be carried through the air across his native land, by day or by night, at twice the flight of a bird."

And so these two men talked about these wonderful classic lands over which they were sailing so serenely, of Zoroaster, the great Persian teacher of other days, of Ahura Mazda, the All-Wise, and the Cobbler of Baghdad, until the tea-bell startled them.

Then, finding they were hungry because the bracing air had made them so, they passed on to the snug little tea-room, where, amid the palm-trees and the orchids, they listened to soft dulcet notes from a small Indian orchestra which accompanied the maharajah. Here, they sipped delicious china tea from dainty Persian cups, and appeased their hunger, as best they could, from the tiny portions of alluring patisserie which usually accompany afternoon tea.

But, later that evening, they did ample justice to a fuller and nobler banquet, which had been prepared for them in the gilded and lofty dining saloon; for they were the honoured guests of the Maharajah of Bangapore. And he entertained them right royally as befitted one of his princely rank.

And in all the wondrous folk-lore and tradition of the ancient Persian kings, was there ever a more regal banquet, or one more conspicuous by the splendour of its oriental wealth than this long-protracted feast? Rich emblazoned goblets of gold, bejewelled with rare and precious gems, adorned the table, for the prince had brought his household treasures; they were to him his household gods, and heirlooms of priceless worth.

Never the Lydian flute played sweeter music than these soft native airs which wandered amid the eastern skies, as, under the silver moon, the long, glistening, pearl-like airship sailed on beneath the stars, while down, far down below, lay the ruins of Persepolis, where the ancient kings of Persia slept their last long sleep.