“Number Two and Number Three are able to succeed, to go on their way unscathed, owing to their notoriety and their assured position. Number Four succeeds for the opposite reason⁠—he succeeds by the way of obscurity. Who is he? Nobody knows. What does he look like? Again nobody knows. How many times have we seen him, you and I? Five times, is it not? And could either of us say truthfully that we could be sure of recognizing him again?”

I was forced to shake my head, as I ran back in my mind over those five different people who, incredible as it seemed, were one and the same man. The burly lunatic asylum keeper, the man in the buttoned-up overcoat in Paris, James, the footman, the quiet young medical man in the Yellow Jasmine case, and the Russian professor. In no way did any two of these people resemble each other.

“No,” I said hopelessly. “We’ve nothing to go by whatsoever.”

Poirot smiled.