After the end of World War II a former P.O.W., Canadian RCAF flyer Laurence Gerard (Powell), returns to France to discover who ordered the killing of his bride of only 20 days, a member of the French Resistance. His father-in-law Étienne Rougon identifies Vichy collaborator Marcel Jarnac. He supposedly died in 1943, but Rougon has strong doubts. Jarnac was so careful about maintaining his anonymity, and the police have no description of him. But his own associate compiled a dossier on him; Gerard finds a burned fragment of it, and an envelope addressed to Madame Jarnac. From this he manages to track the widow to Buenos Aires, Argentina.