Les diaboliques is a 1955 French psychological horror thriller film directed by Henri-Georges Clouzot, starring Simone Signoret, Véra Clouzot, Paul Meurisse and Charles Vanel. It is based on the novel She Who Was No More (Celle qui n'était plus) by Pierre Boileau and Thomas Narcejac.

The story blends elements of thriller and horror, with the plot focusing on a woman and her husband's mistress who conspire to murder the man; after the crime is committed, however, his body disappears, and a number of strange occurrences ensue. The film was the 10th-highest grossing film of the year in France, with a total of 3,674,380 admissions. The film also received the 1954 Louis Delluc Prize.

Clouzot, right after finishing The Wages of Fear, optioned the screenplay rights, preventing Alfred Hitchcock from making the film. This movie helped inspire Hitchcock's Psycho. Robert Bloch himself, the author of the novel Psycho, has stated in an interview that his all-time favorite horror film is Les Diaboliques.

Henri-Georges Clouzot (20 November 1907 – 12 January 1977) was a French film director, screenwriter and producer. He is best remembered for his work in the thriller film genre, having directed The Wages of Fear and Les Diaboliques, which are critically recognized as among the greatest films from the 1950s. Clouzot also directed documentary films, including The Mystery of Picasso, which was declared a national treasure by the government of France.

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