"The Mystery of the Blue Train" is a detective novel by Agatha Christie, featuring her famous Belgian detective Hercule Poirot. It was first published in 1928. Here are some key points about the novel:

1. Plot: The story revolves around the murder of American heiress Ruth Kettering, who is found dead in her compartment on the Blue Train, a luxury train traveling from London to the French Riviera. Poirot, who happens to be on the same train, takes on the case to uncover the killer.
2. Characters: Besides Hercule Poirot, the novel features his friend Katherine Grey, who becomes involved in the mystery, as well as an array of suspects including Ruth's husband Derek Kettering, her lover Count de la Roche, and her maid Ada Mason.
3. Themes: The book explores themes of love, jealousy, greed, and the consequences of one's actions. It also delves into the lifestyles of the wealthy and privileged.
4. Reception: While the novel was generally well-received, some critics felt that it was not Christie's best work. The author herself was reportedly dissatisfied with the book.
5. Adaptations: The novel has been adapted for television and radio, including a 2005 episode of the series "Agatha Christie's Poirot" starring David Suchet.

"The Mystery of the Blue Train" showcases Christie's signature style of intricate plotting, red herrings, and surprising revelations, making it an enjoyable read for fans of classic detective fiction.