“They were the plans of both the tidal engine and the mill machinery that I was glancing over, you asked me to verify your figures, you know,” was the answer. “But he didn’t get any.” The excitement was extreme while it lasted, but it was over now. Inquiries developed the fact that none of the employees in the office had seen the mysterious red-haired stranger enter or leave. He had been evolved out of thin air, it seemed, and had vanished into the same element. That he had had his trouble for his pains was evident, for a careful check-up showed that none of the tidal engine papers was missing, nor had any of the mill machinery plans been taken from Mr. Swift. “How about my chest of stuff?” asked Tom anxiously. “It’s all right,” his father informed him. “I looked at that as soon as I felt able. It’s locked and still in place.” “Good!” cried Tom. “And now we must get busy and solve this mystery.” Making sure that his father, Rad and Mrs. Baggert were really in no danger, Tom took a bath to remove some of the grime of his recent experiences and then sent a couple of his men over to the pine tree in which the _Hummer_ had lodged. “I’m afraid the plane’s a goner,” Tom said. “But maybe you can save part of her. The engine ought to be good, anyhow.” This having been done, and as it was now late in the day, Tom closed the office, first, however, arranging to have Koku take up his sleeping quarters there to be on guard every night. “If the red-haired chap returns, he’ll meet with a different reception this time,” Tom said to Ned. He and Ned made a careful check-up on all the incidents connected with the attempted robbery and assault. They looked about the place for clews, but found none of any moment. Nor could any one be found who had seen the scoundrel make his way to Mr. Swift’s room. The young inventor had not forgotten what Mary had told him about the conversation in the restaurant, and he called up the proprietor on the telephone. But that individual could give him no information concerning the fellows who had had their meal there. It was natural that Tom’s mind should jump to the latest acquisition to his working force—the man Barsky. Somewhat suspicious of him from the first, and these suspicions added to by his father’s ominous shake of the head and his expressed doubts of the Russian, Tom decided to keep an eye on the fellow. It was almost closing time in the shops when Dr. Clayton had gone, leaving all his patients in good shape, and when Tom and Ned had been informed as to the main points in the matter. With his suspicions fermenting, Tom hurried over to the pattern shop. It was with mingled feelings that he saw Barsky hard at work on certain important models. Tom passed the fellow and spoke to him, saying casually: “It will soon be quitting time.” “Eet matters not to me—hours,” replied the man in his strong accent. “When I work I think not of time. I am of much interest in my profession.”