English secret agent Charles Dobbs (James Mason) is shocked to discover that a government official whom he knew has committed suicide. Suspicious circumstances soon point to the death being a murder, and Dobbs investigates further, contacting the victim's wife, Elsa Fennan (Simone Signoret), a survivor of a concentration camp. Despite pressures from senior officials to leave the case, Dobbs continues, hiring veteran cop Inspector Mendel to dig deeper.