But the whistle brought no response, and for a moment the two looked at each other without speaking. Then Bill broke the silence: “Something’s happened and we’ve got to find out what. We must look for signs.” But a thorough search all about the camp revealed nothing. There was not the slightest sign of a struggle and nothing was missing except Gordon. “He must have gone somewhere of his own accord,” Rogers declared. “I can’t picture him being carried off without putting up a fight and you couldn’t put up much of a scrap without leaving some indication of it.” “But why should he go away and leave things to guard themselves? That isn’t like Gordon.” “That’s true too, but——” “I used to think I was pretty good at reading signs in the woods and following trails and all that sort of thing,” Bill interrupted, “but I can’t make a thing out of this mess. There’s absolutely nothing to read so far as I can see.” “Try that whistle once more.” Bill obeyed but there was no response and for several minutes neither spoke. Never, perhaps, had Bill been so worried. The disappearance of his brother coming so soon after the attempt on his life seemed most ominous, and he felt so helpless not knowing which way to turn. “Well, we’re not getting anywhere standing still and thinking about it,” he finally declared. “Gordon never went off and left his post without some good reason and, in spite of the fact that we can find nothing to indicate it, I believe he was carried off.” “What will we do?” “We’ll take the plane and see what we can find.” Bill quickly took two of the cells from their hiding place and in another minute threw over the switch. But, greatly to his surprise, nothing happened. “Maybe there is a sign after all,” he said as he started the search for the trouble. “Wires are all right,” he declared after a short inspection. “I can’t see——yes I can too, here’s the trouble. The brushes are gone from this commutator. Now what do you know about that? Must have been done by someone that knows something about a motor.” “How about the brushes in the other motor?” “They’re all right.” “Then we can go straight up?” “Tell you in a minute.” Bill threw on the switch of the elevator and the propeller at once began to revolve. “Yep, it’s all right,” he announced. “But a lot of good it’ll do us.” “How about changing those brushes? Won’t they fit the other motor?” “They’ll fit all right but there’s no chance to get off the ground here without the elevator, it’s too rough.” “That’s so too.” “If we were only down on the beach we could do it.” “Couldn’t we push it down?” “In about a day’s time.” “Sure you haven’t any spare brushes?” “It’s just possible Gordon put some in the tool kit. I know I didn’t. I’ll take a look. We sure are in luck,” he announced a moment later. “Here’s a half dozen new ones. Now just a minute and I’ll have them in.” Ten minutes later they were in the air and ready to start the search.