Someone Behind the Door is based on the French novel by Jacques Robert "Quelqu'un derriere la porte". In the novel the neurosurgeon (played by Anthony Perkins) is a writer and the Mystery Man 'behind the door'(Charles Bronson) is a fictitious character from the novel he's writing. The novel's fantasy world of writing became the movie's realistic and dramatic psychological duel between Perkins and Bronson.