Based on a John le Carre novel and directed by Sidney Lumet, The Deadly Affair is a cold war thriller centred in the world of espionage. When foreign Office official Samuel Fennan and his wife (Simone Signoret) are anonymously accused of Communist affiliations, their world is turned upside down. Fennan is subsequently found dead from an apparent suicide, although Secret Service agent Charles Dobbs (James Mason) suspects otherwise. When Dobbs' suspicions hit a dead end with his superior officer, the veteran agent decides to resign his government post and join forces with retired CID inspector Mendel (Harry Andrews). As the two men continue their pursuit of the truth, their investigation unearths a spy ring and much more than they ever expected along the way.