"We sure were," was the response; "the question now is, what is that fellow up to?" "Some sort of mischief, just as we surmised," was the reply. "Let's do an Indian crawl toward the shed and see what we can find out." The next instant both boys were noiselessly wriggling their way on their stomachs toward the shed into the interior of which Barton had, by this time, vanished. It was easy work to make a noiseless advance over the soft sand, but so thoroughly had both the Boy Scouts practiced the maneuver of silent advance that even had the ground been different, it is likely that they could have approached unheard. Right up to the very walls of the shed they wriggled their way and then, placing their eyes to a crack in the timbers, they peered in. By the yellow light of a lantern Barton had lighted they saw him dive down into the interior of the submarine and emerge, ere long, with several rolled sheets of paper. The fellow did not appear to labor under anxiety that he was being watched, for he went boldly about his business, taking no apparent pains to screen the light or to move noiselessly. Having emerged from the submarine and reached once more the door of the shed, he extinguished the light and glided out into the night like a half-embodied form. Merritt half leaped to his feet as he saw the fellow making off, but Rob drew his companion down into their place of concealment with a whispered, "Hold on. Don't spoil everything now by betraying our presence. Let him get a little way and we'll follow him." "But we may lose him in the darkness," objected Merritt. "I scarcely think so," was the rejoinder; "in fact, I have a pretty good idea where he is bound for." "And where may that be?" "The place in which he lay this afternoon to read those signals from the distant island. Depend upon it, he is going to meet the men who manipulated that flag!" "By hooky! That's so, Rob. What a mind you have for figuring out things! Of course, it's plain enough now that he is betraying Mr. Barr by giving drawings and plans of the submarine to Mr. Barr's enemies, but I didn't think he'd take so bold a method." "There's nothing very bold about it," retorted Rob. "He is a trusted man, and has been given every opportunity to be dishonest, if it so suits him." "I guess that's right; but it's our duty to thwart him." "You just bet it is, and we'll do it, too, if it's possible. See, there he goes over the top of that sand dune. I could see his figure silhouetted against the sky. I reckon it's safe now to take after him." "All right, you say when." "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."