“Ah, no, indeed,” said Poirot. “You should ask yourself the question that I did. If the good doctor is concealing the young man, what place would he choose? It must necessarily be somewhere near at hand. I think of Cranchester. A hotel? No. Lodgings? Even more emphatically, no. Where, then? Ah! I have it. A nursing home. A home for the mentally unfit. I test my theory. I invent a nephew with mental trouble. I consult Mademoiselle Sheppard as to suitable homes. She gives me the names of two near Cranchester to which her brother has sent patients. I make inquiries. Yes, at one of them a patient was brought there by the doctor himself early on Saturday morning. That patient, though known by another name, I had no difficulty in identifying as Captain Paton. After certain necessary formalities, I was allowed to bring him away. He arrived at my house in the early hours of yesterday morning.”

I looked at him ruefully. “Caroline’s Home Office expert,” I murmured. “And to think I never guessed!”