When we reached the house, my little friend waved aside Mary’s offer of tea.

“No, I thank you, madame. I will mount to my room.”

I followed him. Still frowning, he went across to the desk and took out a small pack of patience cards. Then he drew up a chair to the table, and, to my utter amazement, began solemnly to build card houses!

My jaw dropped involuntarily, and he said at once:

“No, mon ami , I am not in my second childhood! I steady my nerves, that is all. This employment requires precision of the fingers. With precision of the fingers goes precision of the brain. And never have I needed that more than now!”

“What is the trouble?” I asked.

With a great thump on the table, Poirot demolished his carefully built up edifice.