Agatha Christie's Poirot

This episode is based on Agatha Christie's short story The Mystery of the Plymouth Express which first appeared in The Sketch magazine in April, 1923, and was later included in a collection called The Under Dog and Other Stories (1926). In the U.S., the story first appeared under the title The Plymouth Express Affair. The basic storyline for was expanded by Christie to make her full-length novel, The Mystery of the Blue Train (1928).