"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."