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the cipher in a crowded dining-room; and it seemed to me imprudent."

"But, look here, what's the man's game? Why take the thing away and then put it back again?"

"My dear Reeves, you shouldn't go to funerals, it has a depressing effect on your intelligence. The cipher was taken away this morning, when it might have been of some use to you, I suspect, by somebody who had seen me looking at it and so realized that it was important. Then, by a mere accident, it proved that you did not need the paper after all, and had read the message without it. I saw what would happen⁠—if we left your room empty, the cipher, now useless, would be put back. And that is exactly what happened. The hypothesis has become a certainty."

"Good Lord," said Reeves, walking up and down the room. "What on earth are we to do about it?"

"Keep quiet about our movements for one thing. I shouldn't even discuss them with Marryatt more than you can help: he's a little slow-witted, you see, and a little fond of talking, so anything you say to him may get round. Gordon is different⁠—he's all right. The next point is clear. We must set a trap of some kind, and catch our man red-handed."

"You mean the murderer?"

"Not necessarily the murderer. The man who is watching us; it may not be the murderer at all."

"But how do you propose to catch him?"

"I propose that two of us⁠—preferably you and