"I'll give the word right here. Silently, now; remember he is on the outlook for some interference with his plans, and a false move may spoil everything."
"Don't worry about me. A first class Scout should be able to carry through a simple little thing like this."
"Don't be too sure it's simple," admonished Rob, as they silently rose from their crouching postures and took after the vague shadow; "this thing may turn out to be bigger than we thought."
"Have you laid any plans as to what you will do if we do apprehend him in the act of transferring the plans to Mr. Barr's enemies?"
"Not yet. There's no use crossing a bridge till you come to it."
Through the night the boys pursued their quarry as silently as two snakes. At times they lost sight of him, but always his figure would loom up against the star-sprinkled sky as he topped a sand dune. At length they saw him pause and light the lantern, which he had used in the shed, and which he still carried.
This done, he swung the light twice across his body, after the fashion of a brakeman signalling a train to come ahead.
Instantly, out of the darkness, flashed an answering beacon—a red light. The boys clasped each other's arms. That they were on the brink of an exciting adventure they did not doubt. But in each lad's heart was a firm resolve that, come what might, they would do their duty by Uncle Sam.
"Was that red light shown from the other island?" whispered Merritt.
"No, I am inclined to think it came from that launch we saw sneaking in behind the island this afternoon just before the signalling commenced," was the response.