The Disappearance of Mr Davenheim by Agatha Christie

Poirot bets Japp he can solve the mysterious disappearance of a banker, who nipped out to post some letters, without even leaving his own apartment.

The story was first published as a book in the collection Poirot Investigates, 1924, by Bodley Head. The story was adapted for the TV series Agatha Christie’s Poirot in 1990, starring David Suchet, and like many of the other early episodes, included the characters of Hastings, Japp and Miss Lemon, regardless of whether or not they appeared in the original text.