In the devastated city of Berlin during the year 1947, US Congresswoman Phoebe Frost embarks on a mission to investigate the morale of American occupation troops. These soldiers are rumored to be suffering from a strange condition known as "moral malaria," a reflection of the chaos and corruption that pervades the occupation zone. In this environment, soldiers exploit shortages and manipulate local women to gain favors, with officials justifying such behavior, asserting that it is unrealistic to expect them to exhibit both bravery and wisdom.
Phoebe arrives with a birthday cake for Captain John Pringle, the boyfriend of one of her constituents. However, instead of sharing the rare treat with his fellow soldiers, John opts to trade the highly coveted chocolate cake on the black market, ultimately exchanging it for a mattress—a transaction that ends up benefitting his lover, Erika von Schlütow. Meanwhile, the Military Police come knocking at Erika's door, seeking to interrogate her about her past. Despite her previous sentence to a labor camp due to her affiliations, Erika has managed to evade her fate by securing a job at a nightclub through John's influence. When authorities insist she report to the de-Nazification office, John is quick to dismiss their concerns.
As Phoebe immerses herself in Berlin's war-torn backdrop, she observes the numerous American soldiers mingling with local women. Although their tour guide attributes this phenomenon to the soldiers' charm, Phoebe finds herself questioning who is truly influencing whom. Breaking away from the guided tour, she is mistaken for a local by a couple of GIs and pretends to speak only broken English, joining them at Club Lorelei, the local troops' popular haunt. It is here that she encounters cabaret singer Erika von Schlütow, who is rumored to have connections with high-ranking Nazi officials and is now cushioned by the protection of an unidentified American officer. Unbeknownst to Phoebe, John is currently infatuated with the singer.
After discovering that Erika once appeared with Adolf Hitler in a wartime newsreel, Phoebe's curiosity deepens, prompting her to ask John to help her access Erika's file at army headquarters. In a bid to distract her, John begins to charm Phoebe, who initially resists his advances. Their discussion leads to an examination of morals, with Phoebe lamenting the American soldiers’ behavior with former Nazis. John, intrigued, poses a provocative question about her own romantic history, making her confess a past entanglement with a Southern Congressman who favored her vote over genuine affection. Recognizing this as an opportunity, John escalates his charm offensive, gradually breaking through Phoebe’s defenses.
As tensions rise, Erika confronts John regarding his emotional neglect, and his harsh words lead her to worry about her future connections, perhaps with officers brandishing symbols of communism. John's disbelief and disdain come to a head as he leaves her without a second thought.
Meanwhile, Colonel Plummer keeps a close watch on the unfolding situation, directing John to maintain his relationship with Erika in hopes of finding Hans Otto Birgel, a former Gestapo operative suspected to be hiding in the American zone and threatening John's life.
Tragedy strikes when both Erika and Phoebe are taken into custody during a police raid at Club Lorelei, targeting Germans lacking identification. Using her wits, Erika claims that Phoebe is her cousin, successfully securing Phoebe's release while deftly dodging any scandals about her own past.
In a surprising turn, Erika admits to Phoebe that their entire encounter was a strategic move, now placing Phoebe in John's debt as her protector. However, just as the pieces begin to fall into place, Phoebe is shattered to see John sharing a passionate kiss with Erika, a sight that leaves her feeling humiliated and betrayed.
As Phoebe navigates her mixed emotions at the military airport, awaiting her flight home, Colonel Plummer delivers a dossier revealing John's true mission, which was to use Erika as bait for tracking down Birgel. His paternal concern is evident as he hints at the complexity of John's feelings for Phoebe, underscoring the potential dangers at play.
Just when Birgel makes his move at Lorelei, armed and ready to eliminate John, American soldiers intervene just in time. Unfortunately, Erika is arrested for her role in Birgel's schemes. Nonetheless, with the Colonel's help, Phoebe and John are finally able to reconnect, their lives irrevocably altered by the intricate web of deceit and intrigue they have found themselves ensnared in.
