He was not a moment too soon. Hardly had he gotten the fountain pen adjusted before there came a crackling in his ear. He rested his cane, upright, against the stump, and began to tune his instrument by sliding the cap of the fountain pen in and out. In a second he had tuned it perfectly. The sounds came to him with startling clearness.
"He's near at hand," muttered Henry.
He seized his pencil and wrote down on his map the letters that were sounding in his ear. Then with frantic haste he disconnected his instrument, telescoped his extension cane, and gathered up the different articles and thrust them into his pockets. As rapidly as he could pick his way, he went back to his hidden machine. He fastened the metal cane in place, and got everything ready for a quick start.
Suddenly a faint purring noise came to his ears. "Ah!" muttered Henry, "he's started his motor. He's off in that direction. What shall I do?"
His first impulse was to run at speed toward the purring motor, and to try to locate exactly the position of the hidden wireless station. But discretion showed him that was not wise. The spy might turn his lights on at any moment and Henry would be caught. Then everything was lost.
"I must make sure I can find the place in the daytime," muttered Henry. Carefully he gauged the sound, deciding whence it came. "He's right off there," he said. And with his heel he made a long mark in the turf, pointing straight toward the sound.
Almost before he finished, the sound grew louder and Henry knew the car was advancing. He shrank back into the thicket, dragging his motor-cycle with him. An instant later the roadster rolled softly past, not more than fifty feet distant. In a moment more the car had reached the fence and turned into the highway. Its lights suddenly flashed out and the car went bowling down the road toward Brooklyn.
Henry leaped from the thicket and ran toward the highway, pushing his motor-cycle before him. He paused at the opening in the fence, and with his knife smoothed a space on one of the posts and marked a cross on it with his pencil. Then he ran to the highway, started his motor, and was soon flying down the road in pursuit of the roadster. And as he had come, so he returned, with lights out, until Brooklyn was reached and the streets were once more alive with traffic.
At a safe distance he followed the unsuspecting motorist and saw him turn into a private yard in Flatbush. Instantly Henry dismounted, thrust his wheel behind a hedge that fenced a private residence, and gained a position where he could watch the spy's house. He saw the spy close and lock his garage and enter the house. Stealthily Henry approached and noted the house number. At the corner he got the name of the street. Then he hurried back to his hidden motor-cycle and was soon flying back to his comrades at the eagle's nest.