“I go to London tonight,” he explained. “It is imperative.”

“What?”

“Absolutely. The real work, that of the brain (ah, those brave little grey cells), it is done. I go to seek the confirmation. I shall find it! Impossible to deceive Hercule Poirot!”

“You’ll come a cropper one of these days,” I observed, rather disgusted by his vanity.

“Do not be enraged, I beg of you, mon ami. I count on you to do me a service⁠—of your friendship.”

“Of course,” I said eagerly, rather ashamed of my moroseness. “What is it?”

“The sleeve of my coat that I have taken off⁠—will you brush it? See you, a little white powder has clung to it. You without doubt observed me run my finger round the drawer of the dressing-table?”