They Came to Blow Up America (1943)

German-American Carl (George Sanders) is tapped by the U.S. government to infiltrate the Bund, a Nazi propaganda organization. Though Carl is chastised by his own family for joining the group, he refuses to break cover. He later assumes the identity of a Nazi agent and works his way to the Bund headquarters in Hamburg, Germany. There he encounters Frau Reiter (Anna Sten), the wife of the man whose identity he stole, and she tries to expose Carl as a U.S. operative, putting his life in danger.