The scene is set in post-war Berlin. Susanne Mallison 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, a former lawyer who is being blackmailed into luring to East Berlin a man called Kastner, who is helping refugees to escape to the West. Finding that Susanne is attracted to the 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.