A review by book_concierge
The Mystery of the Blue Train by Agatha Christie

3.0

A cache of rubies that once belonged to Catherine the Great comes into the possession of an American millionaire. He gives them to his daughter - Ruth Kitteridge - who is married to a bankrupt English nobleman. She, however, is still in love with the French scoundrel who frequently scams his "lovers." Meanwhile her husband, Derrick, is having an affair with a French exotic dancer - Mirelle. When Ruth takes the Blue Train to Nice to rendevouz with her lover she, inadvisedly, takes the rubies with her. When the train arrives, she is dead and the rubies are missing. Enter Hercule Poirot, who is at his best, putting together "all his little facts" and rearranging them until the puzzle is complete.

Note: I listened to an audio version, which was a BBC dramatization (not a traditional reading of the text, but more of a radio play).