The most acclaimed adaptation of "Murder on the Orient Express" is the 1974 film directed by Sidney Lumet. It features an ensemble cast, including Albert Finney as Hercule Poirot and notable actors like Ingrid Bergman, Sean Connery, and Lauren Bacall. The film received critical praise for its direction, performances, and faithful representation of Agatha Christie's novel. While a 2017 adaptation directed by Kenneth Branagh also garnered attention, the 1974 version is often regarded as the definitive take on this classic mystery.

In the 1974 film "Murder on the Orient Express," directed by Sidney Lumet, the killer is revealed to be Mrs. Helena Andrenyi, played by Vanessa Redgrave. However, the twist is that she is part of a larger conspiracy; all the characters involved in the murder are revealed to have participated in the killing of the victim, Samuel Ratchett, who was responsible for the kidnapping and murder of a child. Detective Hercule Poirot, portrayed by Albert Finney, uncovers this collective act of justice against Ratchett.

There are three notable film adaptations of Agatha Christie's "Murder on the Orient Express." The first was released in 1974, directed by Sidney Lumet, featuring an ensemble cast including Albert Finney as Hercule Poirot. The second version is a television film from 2001, starring Alfred Molina as Poirot. The most recent adaptation was directed by Kenneth Branagh and released in 2017, with Branagh also portraying Poirot. Additionally, there are various television adaptations and stage productions, but these three are the primary film versions.

"Murder on the Orient Express" is not based on a true story; it is a fictional murder mystery novel written by Agatha Christie, first published in 1934. The story features the famous Belgian detective Hercule Poirot solving a murder aboard the luxurious Orient Express train. While the setting and some historical elements may reflect the period, the plot and characters are entirely creations of Christie's imagination. The novel has been adapted into several films and stage productions, solidifying its place as a classic in detective fiction.