The Plymouth Express

A mining entrepreneur hires Poirot to investigate the murder of his daughter and the theft of her jewels, both of which took place aboard the express train to Plymouth. It is not Poirot's only business on the train; he has also been asked to vet the suitors of an Australian magnate's daughter, which sounds like the easier assignment until the murder makes it awkward. The case sits between family tragedy and professional duty, and the two strands keep tangling. The daughter's death is the kind of news that follows a family around for years, and the episode knows it.

The investigation moves through the carriages one compartment at a time. Jane Mason (Marion Bailey) has plenty to say, while McKenzie (Kenneth Haigh) mostly watches. Rupert Carrington (Julian Wadham) and Florence Carrington (Shelagh McLeod) carry the family's secrets, and the Comte de la Rochefour (Alfredo Michelson) glides through with a title and a smile. Halliday (John Stone) completes the party. Kenneth Haigh's McKenzie is the sort of man who seems to know more than he says, which is the best kind of suspect. Hastings accompanies Poirot, Japp takes the official strain, and Miss Lemon holds the loose ends together without fuss.

Rod Beacham wrote the script with Agatha Christie, and Andrew Piddington directed. The train gives the story a natural shape: a sealed box of suspects moving through the dark, nobody able to leave.

It is a brutal murder handled with the series' usual discretion, and the solution is one of those answers that makes you kick yourself for not seeing it. Trains were always a good home for Christie's puzzles, and this one proves the point without ever leaving the platform. The Plymouth Express is not a grand affair, but it is an honest one, and the claustrophobia of the journey does half the detective's work for him.