“Next time you happen to be alone with Lawrence Cavendish, I want you to say this to him. ‘I have a message for you, from Poirot. He says: “Find the extra coffee-cup, and you can rest in peace!” ’ Nothing more. Nothing less.”

“ ‘Find the extra coffee-cup, and you can rest in peace.’ Is that right?” I asked, much mystified.

“Excellent.”

“But what does it mean?”

“Ah, that I will leave you to find out. You have access to the facts. Just say that to him, and see what he says.”

“Very well⁠—but it’s all extremely mysterious.”

We were running into Tadminster now, and Poirot directed the car to the “Analytical Chemist.”

Poirot hopped down briskly, and went inside. In a few minutes he was back again.