"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!"