Four and Twenty Blackbirds 1400-1600

Poirot is eating out with a friend, Henry, and the conversation turns to people's habits. Henry eats regularly in the restaurant that they are in and he points out a white-bearded man as evidence of his theories. This man eats the same meal there on Tuesdays and Thursdays and always orders much the same items as part of his three-course meal. The waitress brings their meals and confirms Henry's view of the man – except that the previous week he also came in on Monday and ordered things he'd never ordered before. Poirot's curiosity is piqued. Three weeks later, Poirot and Henry meet by chance on a tube train and during the conversation Henry mentions that the bearded man has not been seen for a week.