"No. No, of course it doesn't." Bill gave a sigh of relief. "He's just shielding Mark, what?"
"I wonder."
"Well, isn't that the simplest explanation?"
"It's the simplest if you're a friend of Cayley and want to let him down lightly. But then I'm not, you see."
"Why isn't it simple, anyhow?"
"Well, let's have the explanation then, and I'll undertake to give you a simpler one afterwards. Go on. Only remember the key is on the outside of the door to start with."
"Yes; well, I don't mind that. Mark goes in to see his brother, and they quarrel and all the rest of it, just as Cayley was saying. Cayley hears the shot, and in order to give Mark time to get away, locks the door, puts the key in his pocket and pretends that Mark has locked the door, and that he can't get in. How's that?"
"Hopeless, Watson, hopeless."
"Why?"
"How does Cayley know that it is Mark who has shot Robert, and not the other way round?"
"Oh!" said Bill, rather upset. "Yes." He thought for a moment, "All right. Say that Cayley has gone into the room first, and seen Robert on the ground."
"Well?"
"Well, there you are."
"And what does he say to Mark? That it's a fine
