There was a knock on the compartment door. M. Caux frowned. He opened it about six inches.

“What is the matter?” he said peremptorily. “I cannot be disturbed.”

The egg-shaped head of Katherine’s dinner acquaintance showed itself in the aperture. On his face was a beaming smile.

“My name,” he said, “is Hercule Poirot.”

“Not,” the Commissary stammered, “not the Hercule Poirot?”

“The same,” said M. Poirot. “I remember meeting you once, M. Caux, at the Sûreté in Paris, though doubtless you have forgotten me?”