“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 scour the country before the fellow gets away?”

The sergeant considered for a moment.

“There are no trains before six in the morning; so he can’t get away by rail.  If he goes by road with his legs all dripping, it’s odds that someone will notice him.  Anyhow, I can’t leave here myself until I am relieved.  But I think none of you should go until we see more clearly how we all stand.”

The doctor had taken the lamp and was narrowly scrutinizing the body.  “What’s this mark?” he asked.  “Could this have any connection with the crime?”

The dead man’s right arm was thrust out from his dressing gown, and exposed as high as the elbow.  About halfway up the forearm was a curious brown design, a triangle inside a circle, standing out in vivid relief upon the lard-coloured skin.

“It’s not tattooed,” said the doctor, peering through his glasses.  “I never saw anything like it.  The man has been branded at some time as they brand cattle.  What is the meaning of this?”

“I don’t profess to know the meaning of it,” said Cecil Barker; “but I have seen the mark on Douglas many times this last ten years.”

“And so have I,” said the butler.  “Many a time when the master has rolled up his sleeves I have noticed that very mark.  I’ve often wondered what it could be.”

“Then it has nothing to do with the crime, anyhow,” said the sergeant.  “But it’s a rum thing all the same.  Everything about this case is rum.  Well, what is it now?”