Known as "Cicero" to his Nazi handlers, mercenary spy Ulysses Diello (James Mason) poses as valet to Sir Frederic (Walter Hampden), the British ambassador to Turkey. Learning that widowed Countess Anna Staviska (Danielle Darrieux) is broke and offering her services as a spy, Diello persuades her to stash his ill-gotten gains for him in exchange for putting her back into the luxury she desires. Dreaming of a gentleman's exile in Rio de Janeiro, he pushes the espionage game to the limit.