But he halted in amazement when he reached a point near the center of the room, for he saw, under the threshold of the door that led from the dining-room to his father's office, a weak, flickering beam of light.
The door was tightly closed.

He knew from the fact that no light shone through it except from the space between the bottom of it and the threshold that it was barred, for he had locked the door during the time he was repairing the house, and had satisfied himself that it could not be tightly closed unless barred.

Someone was in the room, too.

He heard the scuffle of a foot, the sound of a chair scraping on the floor.

He stood rigid in the darkness of the dining-room, straining his ears to catch another sound.
For a long time he could hear only muffled undertones which, while they told him that there were two or more persons in the room, gave him no clue to their identity.