“I have been an imbecile,” he said simply. “ Ma foi , I lose my head nowadays. Let us return and continue our journey quietly. With reasonable luck the train will not have gone.”

They were only just in time, the train moving off as Knighton, the last of the three, swung himself and his suitcase on board.

The conductor remonstrated with them feelingly, and assisted them to carry their luggage back to their compartments. Van Aldin said nothing, but he was clearly disgusted at Poirot’s extraordinary conduct. Alone with Knighton for a moment or two, he remarked:

“This is a wild-goose chase. The man has lost his grip on things. He has got brains up to a point, but any man who loses his head and scuttles round like a frightened rabbit is no earthly darned good.”