"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."