The Plymouth Express

A young naval officer on the Plymouth Express finds the 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 Gordon Halliday, an Australian mining magnate who asks Hercule Poirot to investigate.

Poirot and Hastings call on Mr Halliday in Park Lane. Last seen, his daughter was going to a house party in the West Country, carrying her jewels. She travelled by train from Paddington and changed at Bristol for the train to Plymouth. Her maid, Jane Mason, travelled with her in a third-class carriage.

Poirot guesses that the knife used to kill Mrs Carrington has been found by the side of the line and that a paper boy who spoke to Mrs Carrington has been interviewed. Japp confirms that this is exactly what has happened. Japp tells Poirot that one of the jewels has been pawned by a known thief called Red Narky, who usually works with a woman called Gracie Kidd.

Poirot and Hastings return to Halliday's house, where Poirot finds clothes like the ones worn by Mrs Carrington when she was murdered. It is revealed that Mason is Gracie Kidd. She and Red Narky probably murdered Mrs Carrington before Bristol. Gracie rode the train past Bristol dressed in similar clothing to the now-dead woman and bought two items from a newsboy, drawing attention to herself in many ways.