“That is so! Mr. Douglas went round the house every night the last thing before he turned in to see that the lights were right. That brought him in here. The man was waiting and shot him. Then he got away through the window and left his gun behind him. That’s how I read it; for nothing else will fit the facts.”

The sergeant picked up a card which lay beside the dead man on the floor. The initials V.V. and under them the number 341 were rudely scrawled in ink upon it.

“What’s this?” he asked, holding it up.

Barker looked at it with curiosity. “I never noticed it before,” he said. “The murderer must have left it behind him.”

“V.V.—341. I can make no sense of that.”

The sergeant kept turning it over in his big fingers. “What’s V.V.? Somebody’s initials, maybe. What have you got there, Dr. Wood?”

It was a good-sized hammer which had been lying on the rug in front of the fireplace—a substantial, workmanlike hammer. Cecil Barker pointed to a box of brass-headed nails upon the mantelpiece.

“Mr. Douglas was altering the pictures yesterday,” he said. “I saw him myself, standing upon that chair and fixing the big picture above it. That accounts for the hammer.”

“We’d best put it back on the rug where we found it,” said the sergeant, scratching his puzzled head in his perplexity. “It will want the best brains in the force to get to the bottom of this thing. It will be a London job before it is finished.” He raised the hand lamp and walked slowly round the room. “Hullo!” he cried, excitedly, drawing the window curtain to one side. “What o’clock were those curtains drawn?”

“When the lamps were lit,” said the butler. “It would be shortly after four.”

“Someone had been hiding here, sure enough.” He held down the light, and the marks of muddy boots were very visible in the corner. “I’m bound to say this bears out your theory, Mr. Barker. It looks as if the man got into the house after four when the curtains were drawn, and before six when the bridge was raised. He slipped into this room, because it was the first that he saw. There was no other place where he could hide, so he popped in behind this curtain. That all seems clear enough. It is likely that his main idea was to burgle the house; but Mr. Douglas chanced to come upon him, so he murdered him and escaped.”

“That’s how I read it,” said Barker. “But, I say, aren’t we wasting precious time? Couldn’t we start out and scout the country before the fellow gets away?”

The sergeant considered for a moment.