A short walk brought them to the hut which had been the scene of the stirring events of the preceding night. Hardly had they entered the door before Merritt gave a start of surprise and a swift exclamation. "Look! Look there!" he cried. "There's Rob's hat!" Sure enough, lying in a corner was the boy leader's campaign hat, which he had lost in the scuffle with Mike and Gyp. "Well, that shows conclusively enough that he was here last night, and from that upset table and the general look of things, I should imagine there had been a pretty lively scrap here," commented the ensign. "But where can Rob be now?" "Probably fearing discovery if they remained here, the men who have taken the plans and the models carried him off, too." "How will it ever be possible to obtain a clew as to where they have gone?" The ensign's answer appeared enigmatical. "Could you describe the motor boat you saw off here yesterday?" "Well, she was of a very remarkable color--a light green, with a signal mast sticking up amidships. Then, too, her cabin was unusually high." "Good. Such a boat as that ought not to be very hard to locate." "I don't quite understand." "Well, then I'll explain. These waters are fairly well traveled, and by working our wireless we may be able to get into communication with some boat similarly equipped, which may have seen that green motor boat." "Cracky, that's a good idea," cried the admiring boy; "let's go back and try it at once." "Yes, it's small use our waiting about here. The rascals overreached us by getting away as quick as possible. I suppose they didn't want to run any chances of discovery." The return to the _Viper_ was quickly made, and the motor boat was driven back to the Submarine Island at top speed. Barton tried with all his might to overhear what was said in the bow of the boat where the Boy Scouts had gathered; but the ensign was careful to keep his voice low, and then, too, the noise of the engines precluded the machinist from catching a word, hard as he strained his ears. Under the tutoring of Hiram Nelson, the wireless scout, the others had all become fair operators. It was agreed that day and night one of them should be at the apparatus, seeking for news of the green motor boat. It was the ensign's opinion that the craft would not put into a port immediately, fearing a hue and cry, but would cruise about or hide in some little frequented part of the coast. But he hoped that if the wireless "caught" some vessel that had spoken to her, he could at least obtain a line on which direction she had taken. The first "session" at the wireless was taken by Hiram, then came the others in rotation; but when at ten o'clock that night Donald, who had learned wireless on his father's yacht, came on duty, there had come no word from the air of a green motor boat. Several ships had been spoken to, but not one reported anything to give the boys hope.