A young naval officer on the Plymouth express finds the dead body of a woman underneath a seat in his carriage. The woman is identified as the Honourable Mrs Rupert Carrington, née Flossie Halliday, the daughter of Ebenezer Halliday, an American steel magnate who asks Poirot to take the case on. Prior to her marriage she was caught up with an adventurer called Count de la Rochefour but her father took her back to America. She later married Rupert Carrington who proved an unsuitable husband, being a gambler deep in debt. They were about to announce a legal separation. Her will leaves everything to her estranged husband who was away from town at the time of the tragedy.