Nazi officer Kurt Gerstein (Ulrich Tukur), a chemist by training, is assigned to develop a disinfectant to purify water for the German army, but soon discovers that his invention, Zyklon B, is being used to exterminate imprisoned Jews. Horrified, he approaches a number of diplomatic figures with his story, but only Riccardo Fontana (Mathieu Kassovitz), a priest, takes him seriously.
