After a quiet smoke, during which time they carefully re-examined a survey map of the Schwarzwald, they began to talk in low whispers, whilst the sun descended amongst the pines on the western heights, over which they had dragged their weary feet.
"It is my opinion," whispered Keane, "that we are within five miles of that secret aerodrome."
His companion nodded, almost drowsily, although every faculty was kept constantly alert.
"It is just possible that one of these paths leads to the very spot, but it will be necessary to explore them both. We must be extremely careful, however, for this professor is sure to prove a wily opponent. I hope, however, some wood-cutter or peasant may pass this way soon, and that we may learn something from him which will help us," continued the senior airman.
"What if the wood-cutter should prove to be the professor himself?" asked Sharpe, with a humorous twinkle in his eyes.
"It is even possible," returned his companion.
"In that case it would be diamond cut diamond, Keane, eh?"
The other shrugged his shoulder at the very thought, and prayed that such a contingency might not happen, at any rate until something tangible had first been discovered.
"In three hours it will be midnight," he said. "If no one passes this way by then, I think we must carry out our search in the dark. Time is pressing; we must find something within another forty-eight hours, or poor old Tempest will be at his wit's end, and calling us home again. He cannot leave us long on this trail."
"The greater the pity. A fortnight is not too long to follow a trail like this," said Sharpe.