Cayley nodded.  Then he said abruptly, “He’s getting a warrant for Mark’s arrest.”

Bill made a suitably sympathetic noise, and Antony said with a shrug of the shoulders, “Well, he was bound to do that, wasn’t he?  It doesn’t follow that—­well, it doesn’t mean anything.  They naturally want to get hold of your cousin, innocent or guilty.”

“Which do you think he is, Mr. Gillingham?” said Cayley, looking at him steadily.

“Mark?  It’s absurd,” said Bill impetuously.

“Bill’s loyal, you see, Mr. Cayley.”

“And you owe no loyalty to anyone concerned?”

“Exactly.  So perhaps I might be too frank.”

Bill had dropped down on the grass, and Cayley took his place on the seat, and sat there heavily, his elbows on his knees, his chin on his hands, gazing at the ground.

“I want you to be quite frank,” he said at last.  “Naturally I am prejudiced where Mark is concerned.  So I want to know how my suggestion strikes you who have no prejudices either way.”

“Your suggestion?”

“My theory that, if Mark killed his brother, it was purely accidental as I told the Inspector.”

Bill looked up with interest.

“You mean that Robert did the hold-up business,” he said, “and there was a bit of a struggle, and the revolver went off, and then Mark lost his head and bolted?  That sort of idea?”

“Exactly.”

“Well, that seems all right.”  He turned to Antony.  “There’s nothing wrong with that, is there?  It’s the most natural explanation to anyone who knows Mark.”

Antony pulled at his pipe.

“I suppose it is,” he said slowly.  “But there’s one thing that worries me rather.”

“What’s that?” Bill and Cayley asked the question simultaneously.

“The key.”

“The key?” said Bill.

Cayley lifted his head and looked at Antony.  “What about the key?” he asked.

“Well, there may be nothing in it; I just wondered.  Suppose Robert was killed as you say, and suppose Mark lost his head and thought of nothing but getting away before anyone could see him.  Well, very likely he’d lock the door and put the key in his pocket.  He’d do it without thinking, just to gain a moment’s time.”

“Yes, that’s what I suggest.”

“It seems sound enough,” said Bill.  “Sort of thing you’d do without thinking.  Besides, if you are going to run away, it gives you more of a chance.”

“Yes, that’s all right if the key is there.  But suppose it isn’t there?”

The suggestion, made as if it were already an established fact, startled them both.  They looked at him wonderingly.

“What do you mean?” said Cayley.