“We’ll begin at the moment when Mark shoots Robert. Call it an accident; probably it was. Mark would say it was, anyhow. He is in a panic, naturally. But he doesn’t lock the door and run away. For one thing, the key is on the outside of the door; for another, he is not quite such a fool as that. But he is in a horrible position. He is known to be on bad terms with his brother; he has just uttered some foolish threat to him, which may possibly have been overheard. What is he to do? He does the natural thing, the thing which Mark would always do in such circumstances. He consults Cayley, the invaluable, inevitable Cayley. “Cayley is just outside, Cayley must have heard the shot, Cayley will tell him what to do. He opens the door just as Cayley is coming to see what is the matter. He explains rapidly. ‘What’s to be done, Cay? What’s to be done? It was an accident. I swear it was an accident. He threatened me. He would have shot me if I hadn’t. Think of something, quick!’ “Cayley has thought of something. ‘Leave it to me,’ he says. ‘You clear out altogether. _I_ shot him, if you like. I’ll do all the explaining. Get away. Hide. Nobody saw you go in. Into the passage, quick. I’ll come to you there as soon as I can.’ “Good Cayley. Faithful Cayley! Mark’s courage comes back. Cayley will explain all right. Cayley will tell the servants that it was an accident. He will ring up the police. Nobody will suspect Cayley—Cayley has no quarrel with Robert. And then Cayley will come into the passage and tell him that it is all right, and Mark will go out by the other end, and saunter slowly back to the house. He will be told the news by one of the servants. Robert accidentally shot? Good Heavens! “So, greatly reassured, Mark goes into the library. And Cayley goes to the door of the office.... and locks it. And then he bangs on the door and shouts, ‘Let me in!’” Antony was silent. Bill looked at him and shook his head. “Yes, Tony, but that doesn’t make sense. What’s the point of Cayley behaving like that?” Antony shrugged his shoulders without answering. “And what has happened to Mark since?” Antony shrugged his shoulders again. “Well, the sooner we go into that passage, the better,” said Bill. “You’re ready to go?” “Quite,” said Bill, surprised. “You’re quite ready for what we may find?” “You’re being dashed mysterious, old boy.” “I know I am.” He gave a little laugh, and went on, “Perhaps I’m being an ass, just a melodramatic ass. Well, I hope I am.” He looked at his watch. “It’s safe, is it? They’re still busy at the pond?” “We’d better make certain. Could you be a sleuthhound, Bill—one of those that travel on their stomachs very noiselessly? I mean, could you get near enough to the pond to make sure that Cayley is still there, without letting him see you?” “Rather!” He got up eagerly. “You wait.” Antony’s head shot up suddenly. “Why, that was what Mark said,” he cried. “Mark?” “Yes. What Elsie heard him say.” “Oh, that.”