Some quick rejoinder was springing to Derek’s lips, but he checked it as though something in the little Belgian’s twinkling eyes had made him suddenly alert. He spoke carefully, choosing his words.

“Knighton is a very good fellow,” he said.

Just for a moment Katherine fancied that Poirot looked disappointed.

“He is a great admirer of yours, M. Poirot,” she said, and she related some of the things that Knighton had said. It amused her to see the little man plume himself like a bird, thrusting out his chest, and assuming an air of mock modesty that would have deceived no one.

“That reminds me, Mademoiselle,” he said suddenly, “I have a little matter of business I have to speak to you about. When you were sitting talking to that poor lady in the train, I think you must have dropped a cigarette case.”