At the height of the "final solution", SS officer Kurt Gerstein, a chemist by profession, discovers that the gas Zyklon B is being used to exterminate Jews and other political undesirables. Shocked, Gerstein turns to diplomats and clergymen, trying to find someone who will help stop the genocide. But the only one who responds is a young idealistic Jesuit priest, who decides to take Gerstein's story to Pope Pius XII. But the two men only encounter cynicism and indifference. Based on a German play from the 1960s, and partially on real events, Costa-Gavras' film uses the cinema as an arena for testing moral dilemmas.