Night Must FallNight Must Fall is a play, a psychological thriller, by Emlyn Williams, first performed in 1935.
Warning: wikipedia contains spoilers
The 1937 film of the play tells the story of an elderly woman who hires a young man as a companion, despite her niece's worries that he may be a murderer. It stars Robert Montgomery, Rosalind Russell and Dame May Whitty.
The movie was adapted by John Van Druten from the play, and was directed by Richard Thorpe.