"I guess I can sneak up there and take a look in one of the windows," thought the young inventor. He was about to advance, when he suddenly stopped. He heard some one or some thing coming around the corner of the mansion. A moment later a man came into view, and Tom easily recognized him as one of those who had been in the automobile. The heart of the young inventor beat so hard that he was afraid the man would hear it, and Tom crouched down in the bushes to keep out of sight. The man evidently did not suspect the presence of a stranger, for, though he cast sharp glances into the tangled undergrowth that fringed the house like a hedge, he did not seek to investigate further. He walked slowly on, making a circuit of the grounds. Tom remained hidden for several minutes, and was about to proceed again, when the man reappeared. Then Tom saw the reason for it. "He's on guard!" the lad said to himself. "He's doing sentry duty. I can't approach the house when he's there." For an instant Tom felt a bitter disappointment. He had hoped to be able to carry out his plan as he had mapped it. Now he would have to make a change. "I'll have to wait until night," he thought. "Then I can sneak up and look in. The guard won't see me after dark. But it's going to be no fun to stay here, without anything to eat. Still, I've got to do it." He remained where he was in the bushes. Several times, before the sun set, the man doing sentry duty made the circuit of the house, and Tom noted that occasionally he was gone for a long period. He reasoned that the man had gone into the mansion to confer with his confederates. "If I only knew what was going on in there," thought Tom. "Maybe, after all, the men haven't got the model and papers here. Yet, if they haven't, why are they staying in the old house? I must get a look in and see what's going on. Lucky there are no shades to the windows. I wish it would get dark." It seemed that the sun would never go down and give place to dusk, but finally Tom, crouching in his hiding place, saw the shadows grow longer and longer, and finally the twilight of the woods gave place to a density that was hard to penetrate. Tom waited some time to see if the guard kept up the circuit, but with the approach of night the man seemed to have gone into the house. Tom saw a light gleam out from the lonely mansion. It came from a window on the ground floor. "There's my chance!" exclaimed the lad, and, crawling from his hiding place, he advanced cautiously toward it.