The Stranger (1946)

Franz Kindler is one of the most notorious of the Nazis who has escaped capture following the war. Unlike most of his contemporaries, Kindler liked to remain anonymous in carrying out his heinous war crimes, and as such only those closest to him knows what he looks like. Mr. Wilson of the war crimes commission is able to convince his colleagues to release one of Kindler's closest imprisoned associates, Konrad Meinike, who Wilson expects will lead them to Kindler. Wilson is able to follow Meinike to small town Harper, Connecticut. Shortly after his arrival in town, Wilson, with only circumstantial evidence, believes that Kindler is Charles Rankin, a professor at the local boys college. Wilson is correct, Kindler who plans to marry Mary Longstreet, the daughter of Supreme Court Justice Adam Longstreet, to add more respectability to his cover, and who does plan for a Nazi uprising when the time is right. Wilson ends up playing a game of cat and mouse, first with Meinike, then with Rankin, both of the Nazis who know that Wilson is after them. Especially between Wilson and Rankin, the game turns to one of taunts in plain sight, Rankin who believes one of his saving graces being Mary, who probably would not believe him of any such wrongdoing in her love for him. If Mary does get close to discovering the truth, her life and that of those closest to her may be in danger.

IMDb: https://www.imdb.com/title/tt0038991