After her Nazi father faces treason charges from a jury in Miami, Florida, Alicia Huberman seeks to escape her turmoil by hosting a loud party, where she flirts with the uninvited T. R. Devlin. Later that night, while driving under the influence, Alicia is pulled over for speeding. However, upon seeing Devlin's official credentials, the motorcycle officer lets her go without a ticket. Infuriated by Devlin, who she perceives as a traitor, she lashes out at him, calling him a "double-crossing cop."
Despite his disapproval of Alicia's reckless lifestyle, Devlin believes in her loyalty to America, having overheard her private comments. He proposes a covert mission for her to infiltrate a Nazi industrial group in Brazil. At first resistant, the embittered Alicia ultimately decides to join him in Rio de Janeiro. There, she enjoys a week filled with romance and leisure, claiming to Devlin that she is a changed woman. While Devlin remains sceptical of her transformation, he finds himself falling for her.
However, their peaceful time is disrupted when Devlin’s superior, Paul Prescott, reveals that Alicia's mission involves seducing her former love, Alexander Sebastian, to uncover the workings of his war machine. Torn between her feelings and the mission, Alicia feels unloved and accepts her assignment, seeing it as a chance to prove herself. Devlin, seeing her decision as a sign of her capriciousness, steps back, allowing her to pursue Alex.
Their plan unfolds as Alicia meets Alex in a park and flirts with him. During a dinner at Alex's home, she overhears a conversation about a guest, Emil Hupka, whose behavior has drawn unwanted attention. Soon, it becomes apparent that Alex's group—led by the sinister Eric Mathis—plans to eliminate Emil. While reporting back to Devlin at a Rio racetrack, Alicia sarcastically informs him that the lovesick Alex is now her "playmate." Devlin feels disgusted but maintains his cover as Alicia's heartbroken admirer.
Shortly after, Alicia surprises Prescott and Devlin with news of her engagement to Alex, leaving Devlin heartbroken yet again. Following a brief honeymoon, they return to Alex’s home, where his overbearing mother, Anna, regards Alicia with jealousy. Alicia quickly surveys the house and discovers that only Alex has access to the wine cellar's key.
Devlin instructs Alicia to host a party to steal the key, enabling him to investigate the cellar. During the event, she manages to take the key and sneaks away with Devlin. In the cellar, they discover a bottle that, instead of wine, contains a mysterious mineral. While trying to conceal their find, they are caught by Alex, who grows suspicious.
As days pass, Alicia begins to feel increasingly unwell due to Anna’s secretive poisoning—disguised as a coffee additive. During a subsequent meeting with Prescott, Alicia learns about the mineral's true identity: uranium. Though too weak to escape, she realizes the peril she is in due to Alex and Anna's treachery. Devlin, noticing Alicia’s illness, rushes to her aid, determined to rescue her from the clutches of the Nazis.
Finally, Devlin arrives at Alex's residence, where he finds a sedated yet elated Alicia. As they confess their love amidst the chaos, Alex tries to intervene, but Devlin stands firm, sealing his rival's fate as he prepares to take Alicia to safety.
