Marcello Clerici (Jean-Louis Trintignant) is a member of the secret police in Mussolini's Fascist Italy. He and his new bride, Giulia (Stefania Sandrelli), travel to Paris for their honeymoon, where Marcello also plans to assassinate his former college professor Luca Quadri (Enzo Tarascio), an outspoken anti-Fascist living in exile. But when Marcello meets the professor's young wife, Anna (Dominique Sanda), both his romantic and his political loyalties are tested.