Tom, who had been sitting on a log under a bush, staring at the lake, arose.  He was feeling rather weak and faint, and was at a loss to account for it, until he remembered that he had had no dinner.

“And I’m not likely to get any,” he remarked.  “I’m not going to eat until I see who’s in that house.  Maybe I won’t then, and where supper is coming from I don’t know.  But this is too important to be considered in the same breath with a meal.  Here goes.”

Cautiously Tom made his way forward, taking care not to make too much disturbance in the bushes.  He had been on hunting trips, and knew the value of silence in the woods.  He had no paths to follow, but he had noted the position of the sun, and though that luminary was now sinking lower and lower in the west, he could see the gleam of it through the trees, and knew in which direction from it lay the deserted mansion.

Tom moved slowly, and stopped every now and then to listen.  All the sounds he heard were those made by the creatures of the woods—­ birds, squirrels and rabbits.  He went forward for half an hour, though in that time he did not cover much ground, and he was just beginning to think that the house must be near at hand when through a fringe of bushes he saw the old mansion.  It stood in the midst of what had once been a fine park, but which was now overgrown with weeds and tangled briars.  The paths that led to the house were almost out of sight, and the once beautiful home was partly in ruins.

“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.