“I fancy he can. There is undoubtedly a real Dr. Quentin who is probably abroad somewhere. Number Four has simply masqueraded as him for a short time. The arrangements with Dr. Bolitho were all carried out by correspondence, the man who was to do locum originially having been taken ill at the last minute.”

At that minute, Japp burst in, very red in the face.

“Have you got him?” cried Poirot anxiously.

Japp shook his head, very out of breath.

“Bolitho came back from his holiday this morning⁠—recalled by telegram. No one knows who sent it. The other man left last night. We’ll catch him yet, though.”

Poirot shook his head quietly.

“I think not,” he said, and absentmindedly he drew a big 4 on the table with a fork.