Before very long the prow of the boat grated on a sandy beach, and the two men, gathering up some rolls of paper and several bulky-looking objects, left the craft, first securing it by an anchor and line. As their footsteps died away, Rob ventured to raise his head above the gunwale of the boat and follow them with his eyes. He saw them ascend the beach and enter the hut, apparently a structure once used by fishermen or hunters. After an interval a light shone from the solitary window of the hut, and Rob came to a sudden resolve to find out just what was going forward. With this object in view he clambered out of the boat, taking every precaution against making unnecessary noise. On hands and knees he then approached the lighted window. The night was dark, and, standing at a fair distance from the casement, he did not feel much fear of being seen from within. It is hard for persons in a brightly lighted chamber to perceive what is going on outside. Seated around a rough table in the hut, which consisted of only one room, Rob saw three men. Two of them, undoubtedly, were those who had unconsciously rowed him to the island. The other he recognized with a start as the possessor of the face which had peered through the transom on the memorable night in Hampton, when plans for the experiments on the island were in process of being formulated. In other words, the third member of the party was none other than Nordstrom Berghoff, the spy. Instantly many things that had been vague to Rob crystallized into a clear understanding of the situation. The signals from the island, the indignation of Barton over the presence of the Boy Scouts, and the stealing of the plans and models, all stood out plainly now as being part of an elaborate plot of which Berghoff was the mainspring. A wave of indignation swept over the boy as he contemplated the rascals within the hut gloating over the things they had obtained from the treacherous Barton. "The scoundrels," he thought; "so they think they can rob Uncle Sam of one of the greatest submarines ever invented, and do so with impunity! I don't care what happens, I'll fool them if I can." With this resolve firmly embedded in his mind, Rob crept closer to the window. By skillful maneuvering he was at last almost under the casement. In this position every word uttered within the hut was clear to him. He heard Berghoff chuckling gleefully over the manner in which the night's work had been carried out. "Undt not a vun of dose Boy Scouts knew anting aboudt idt," he exclaimed. "No," rejoined one of his companions, a swarthy man with a pallid face on which there stood out a bristly beard; "those kids were out of the game so far as we were concerned. That Barton is a slick one, all right." "Well, he's getting well paid for the job," struck in the third man, who was short and stocky, with a crop of rough, reddish hair and a protruding chin that gave him a "bull doggy" aspect.