Rich and unhappily married Ruth Kettering receives from her father a priceless and famous ruby, with a warning to never take it with her abroad lest she runs into danger. Unfortunately she embarks on Le Train Bleu towards the French Riviera with the ruby and is soon found strangled in her compartment. But Hercule Poirot was also on the train and begins to investigate the crime (with assistance from the french police) which, as always, is more than first appears.
Other characters include Katherine Grey, another passenger of the train, a young woman who received an unexpected inheritance and is travelling abroad for the first time, Ruth's estranged and ill-tempered husband, Derek Kettering, a cabaret dancer named Mirelle, the womanizing Comte de la Roche, the Marquis (a famous jewel thief who has never been identified), Ruth's millionaire father Rufus Van Aldin, desperate to find his daughter's murderer, and Van Aldin's secretary Major Knighton.
It was adapted for television in 2006 in an episode of Agatha Christies Poirot.
This novel provides examples of:
- The Alibi: Of course. The Comte has one. Derek Kettering doesn't.
- All Girls Want Bad Boys: Somewhat complicated for Katherine Grey as she isn't sure who is the Bad Boy.
- Bitch in Sheep's Clothing: Every man in the book sees right through the Comte. Not the women.
- The Casino: Much of the action takes place in the gardens or gaming rooms of the casino at Monte Carlo.
- Cool Train: Le Train Bleu, the luxury overnight service across France from Calais to Nice.
- Fake Aristocrat: the 'Comte' de la Roche
- The Fashionista: The first thing Katherine does upon inheriting her fortune is march into a fancy French atalier and order a cutting edge wardrobe. Understandable as she'd never had enough money for nice clothes before.
- Gold Digger: 'Chubby' Evans clearly only married to Lady Tampling for her money. That said he keeps his side of the bargain by being a charming, faithful and not too extravagant husband. Mireille, Derek Kettering's former mistress is a much less sympathetic example.
- Idle Rich: Most of the cast is either this, aspires to it or pretends to be it.
- I Never Said It Was Poison: Poirot wonders how Derek Kettering knows Ruth's rubies were stolen. He also wonders how Mirelle knows the time of death.
- Marriage of Convenience: What Derek and Ruth Kettering had. Derek describes it as a perfectly fair bargain that failed due to faults on both sides.
- Phantom Thief: The Marquis has this reputation.
- Pretty in Mink: Ruth Kettering's full length mink coat proves unexpectedly important.
- Sharp-Dressed Man: Poirot is of course famous for his dress sense, and the Comte is equally well dressed.
- Spanner in the Works: Knighton is undone because he left his cigarette case in Ruth Kettering's compartment, and then fell in love with Katherine Grey.
- Spoiled Brat: Our victim. Everybody but her loving father can see it. That said she wasn't bad enough to count as an Asshole Victim.
- Thriller on the Express: Although only the murder and the initial investigation take place on the train.
- Til Murder Do Us Part: The fact that Ruth was about to divorce him and her death left him heir to her millions makes Derek the obvious suspect.
- The Watson: Katherine Grey serves as this to Poirot in this novel.
- What Beautiful Eyes!: Just about every man in the book is entranced by Katherine's clear grey eyes.
- Also, comments on Poirot's bright green eyes.
- The Vamp: Mireille.
- Villainous Crossdresser: Ada Mason is actually Kitty Kidd, an actress who specialized in male impersonation. Part of the murder plot involves her leaving the train in Lyons, disguised as a man.
- Your Cheating Heart: Ruth and Derek Kettering are both unfaithful, with the Comte de la Roche and Mirelle, respectively.