“Yes,” said Poirot thoughtfully, as he put away the brush, “one must not permit oneself to be obsessed by one idea. I have been in danger of that. Figure to yourself, my friend, that even here, in this case, I am in danger of it. Those two lines you mentioned, a downstroke and a line at right angles to it, what are they but the beginning of a 4?”

“Good gracious, Poirot,” I cried, laughing.

“Is it not absurd? I see the hand of the Big Four everywhere, it is well to employ one’s wits in a totally different milieu. Ah! There is Japp come to meet us.”