"A man! In the machine shop!" exclaimed Tom, rising from his chair. Mr. Swift also got up, and the two hurried from the house. As they reached the yard they saw a man emerging from the building where Mr. Swift was constructing his turbine motor. The man had his back turned toward them and seemed to be sneaking around, as though desirous of escaping observation. "What do you want?" called Mr. Swift. The man turned quickly. At the sight of Mr. Swift and Tom he made a jump to one side and got behind a big packing-box. "That's queer," spoke Tom. "I wonder what he wants?" "I'll soon see," rejoined Mr. Swift, and he started on a run toward where the man was hiding. Tom followed his father, and as the two inventors reached the box the man sprang from behind it and down the yard to a lane that passed in back of the Swift house. As he ran he was seen to stuff some papers in his pocket. "My plans! He's stolen some of my plans!" cried Mr. Swift. "Catch him, Tom!" Tom ran after the stranger, whose curious actions had roused their suspicions, while Mr. Swift entered the motor shop to ascertain whether anything had been stolen. CHAPTER IX. A FRUITLESS PURSUIT Down through the yard Tom speeded, in and out among the buildings, looking on every side for a sight of the bold stranger. No one was to be seen. "He can't be very far ahead," thought Tom. "I ought to catch him before he gets to the woods. If he reaches there he has a good chance of getting away." There was a little patch of trees just back of the inventor's house, not much of a woods, perhaps, but that is what they were called. "I wonder if he was some ordinary tramp, looking for what he could steal, or if he was one of the gang after dad's invention?" thought Tom as he sprinted ahead. By this time the youth was clear of the group of buildings and in sight of a tall, board fence, which surrounded the Swift estate on three sides. Here and there, along the barrier, were piled old packing-cases, so that it would be easy for a fugitive to leap upon one of them and so get over the fence. Tom thought of this possibility in a moment. "I guess he got over ahead of me," the lad exclaimed, and he peered sharply about. "I'll catch him on the other side!" At that instant Tom tripped over a plank and went down full length, making quite a racket. When he picked himself up he was surprised to see the man he was after dart from inside a big box and start for the fence, near a point where there were some packing-cases piled up, making a good approach to the barrier. The fugitive had been hiding, waiting for a chance to escape, and Tom's fall had alarmed him. "Here! Hold on there! Come back!" cried the youth as he recovered his wind and leaped forward.