A prim Congresswoman gets caught up in the romantic decadence of post-war Germany.

In 1947, United States Congresswoman from Iowa, Phoebe Frost, arrives in the American occupation zone in Berlin, Germany, with a group of fellow congressmen to investigate the morale of the ten thousand troops stationed there. The congressmen receive an official greeting from American troops, during which Phoebe presents to Captain John Pringle a home-baked cake, which was sent by his fiancée, whom he has not seen in four years. Unknown to Phoebe, John immediately trades the cake on the black market for a mattress, and brings the mattress and various hard-to-find luxury items to his German girl friend, Erika von Schluetow, a beautiful torch singer. After a tour of the city, the stern and prim Phoebe immediately begins taking notes on the troops playtime antics, which include chasing German blondes in the ruined streets and drinking at an off-limits nightclub called the Lorelei. After being mistaken for a young German woman by a pair of rowdy American soldiers, Phoebe accompanies them to the club, where Erika sings. The soldiers tell Phoebe that although Erika is suspected of having been the girl friend of a Nazi leader--either Hermann Goering or Joseph Goebbels--she is now receiving protection from an American officer. Unknown to Phoebe, the officer is John. Phoebe sees the cake being served at the Lorelei and confiscates it, then appoints John to watch Erika's apartment in order to catch her American lover. The next day, after seeing Erika speaking to Adolph Hitler in a newsreel shot during the war at a Berlin opera house, Phoebe accompanies John to army headquarters to retrieve Erika's official file. To keep Phoebe from accessing the file, John pretends to be in love with her, and chases her around the file cabinets for a kiss. After nervously reciting Longfellow's poem "The Midnight Ride of Paul Revere" to avoid him, Phoebe relents and passionately kisses him. She immediately falls in love, and within forty-eight hours, John has proposed in order to distract her from pursuing Erika. Erika, meanwhile, asks John to take her to America with him, and he begins to see how manipulative she is. Later, Phoebe dresses up in an elegant gown she got on the black market and goes out with John to the Lorelei, where Erika insults her. Phoebe then announces that she has arranged a furlough for John so that they can marry. After John is called away to report to his colonel, Rufus J. Plummer, Erika and Phoebe are caught in a police raid that is conducted to catch Germans without proper papers. At army headquarters, Plummer warns John that he has been "wise to him" all along before ordering him to stay away from the congresswoman and aggressively court Erika. Plummer hopes to ferret out one of Erika's lovers, a jealous ex-gestapo agent named Hans Otto Birgel, who is thought to be hiding in the American occupation zone. Meanwhile, at the police station, Erika convinces Phoebe not to embarrass the Congress by identifying herself, and gets Phoebe released by saying she is her cousin. Phoebe, thinking Erika has befriended her, goes with her to her apartment, where Erika tells her that John is her mysterious lover and has been pretending to be in love with Phoebe merely to shield Erika. Heartbroken, Phoebe cries, then hides as John enters and tells Erika that his romance with Phoebe was just a ruse. Phoebe then steps out from the shadows and leaves, humiliated. Plummer later delays the congressmen's departure to arrange for John and Phoebe's reconciliation, and in his jeep on the way back from the airfield, tells the group that he appointed John as a "love commando" in order to bring in Birgel. Meanwhile, Birgel surreptitiously enters the Lorelei armed with a gun, and takes aim at John. American soldiers on watch fire first, however, and when Plummer's jeep arrives and Phoebe, who now realizes that John was never really in love with Erika, rushes in to see who was killed, Birgel is revealed dead on the nightclub floor. Plummer has Erika arrested to serve time in a labor camp, and when she tries to use her feminine wiles to manipulate him into releasing her, the formidable colonel tells her that he has just become a grandfather. Determined to marry John, Phoebe corners him in the nightclub for a kiss, and, hiding behind barroom chairs, he recites "The Midnight Ride of Paul Revere."