The moral no-man’s-land of illegal immigration in London proves fertile ground for modern noir in this superior suspense film, directed by Stephen Frears (The Grifters) from a screenplay by Steve Knight. A doctor who’s fled Nigeria for political reasons (Chiwetel Ejiofor in a fine performance) is reduced to driving a cab by day and working the front desk of a posh hotel by night; after he discovers a human heart in a hotel-room toilet, his ice-cold Latino boss (Sergi Lopez) uses the promise of a passport to lure him into appalling black-market activities. Audrey Tautou (Amelie) is unconvincing as the doctor’s young Turkish friend, and the story’s too-neat climax strains the limits of credibility. But for the most part the film is an impressive mix of entertainment and social comment, spinning a great mystery even as it confronts an ugly world. R, 107 min.