The scene is post-war Berlin. Susanne Mallison (Claire Bloom) arrives in the city to stay with her brother and his German wife, Bettina. Reluctantly, Bettina takes Susanne into the Eastern Sector where they meet Ivo Kern (James Mason), a former lawyer who is being blackmailed into luring a man called Kastner to East Berlin, who is helping refugees to escape to the West. Sensing Susanne's attraction to the rogue ex-lawyer, Bettina confesses that she is married to Ivo, whom she thought to be dead. He has recently reappeared and is forcing her help in his plot to capture Kastner.