A Foreign Affair (1948) on Netflix

A US congressional committee is in Berlin following World War II to investigate rumors of low morale amongst the American troops patrolling the American quadrant of the city. One of those on the committee is Congresswoman Phoebe Frost, a Republican from Iowa who has a singular focus on work, especially when on a mission. Once in Berlin, she believes the committee's military liaison, Colonel Rufus J. Plummer, is providing them with a false report of the issue as she herself has witnessed firsthand what she considers the depravity occurring in the city, especially between American troops and German "fraulein". Specifically, she is concerned about an unofficial report of Erika von Schlütow, a singer at an underground cabaret, who was a high ranking Nazi during the war and whose record is being protected and expunged by a high ranking but unknown American military man. To find out who this military man is, Phoebe enlists the help of Captain John Pringle, a fellow Iowan who she met on her travels in Berlin and who she trusts because of his Iowa heritage. She is however unaware that John is Erika's lover and protector. John does whatever he needs to to keep this secret from Phoebe for the few days she's in town. His measures include pretending to have a romantic interest in her himself. Phoebe comes to her own incorrect conclusion of who is protecting Erika. Erika, on the other hand, has her own agenda which she demonstrates in an encounter with Phoebe. Meanwhile, John's secret from Phoebe may become compromised when Colonel Plummer, aware of John and Erika's relationship, asks John to perform a military task concerning hunting down Hans Otto Birgel, a missing member of the Gestapo who was a former companion of Erika's.