When Johnny Farrell, a callous young gambler new to the Argentine, is held up in a dark alleyway by a thief who demands his money or his life, a sinister man steps from the shadows and banishes the robber with a knife he has concealed in his walking stick. The man then directs Johnny to a posh Buenos Aires casino, where he then enjoys a winning streak. Johnny is cashing in his chips when he is summoned to the office. There, he is met by the man from the alley who, after introducing himself as Ballin Mundson, the owner of the casino, accuses Johnny of cheating. When Johnny proposes that he work for the casino, Ballin hires him with the warning that gambling and women don't mix. Johnny quickly wins Ballin's confidence, and one day, soon after the end of World War II, Ballin grimly informs Johnny that he is leaving on a trip and appoints Johnny casino manager. Several weeks later, Ballin returns, beaming, and introduces Johnny to his alluring new wife, Gilda. Johnny is stunned to discover that Ballin has married his erstwhile sweetheart, the woman he now loathes as much as he once loved. Although Ballin is unaware of their former relationship, Uncle Pio, the philosophical washroom attendant, senses their passion. That night, Obregon, an agent of the secret police and a constant observer at the casino, introduces himself to Johnny. As Ballin holds a disagreeable meeting with two Germans, Gilda flirts with one of the customers, thus inflaming her husband's jealousy. Gilda and Johnny's hostile repartee finally prompts Ballin to suspect their previous alliance, and he cruelly offers a toast, wishing disaster to the "wench" who wronged Johnny. After Ballin appoints Johnny as Gilda's watchdog, Gilda taunts him by continuing her flirtations with other men. Ballin, who covertly controls a tungsten cartel, is visited one day by a man he has driven out of business. After Ballin ignores his entreaties, the man fires a gun at Ballin, misses and then shoots himself as Obregon silently watches. Questioned by Johnny about the incident, Ballin shows him the safe he has hidden in his office and provides him with the combination. As Johnny continues to hide Gilda's indiscretions, his hatred toward her deepens. One night, Gilda admits to Johnny that she married Ballin on the rebound from him, but her confidence only inflames his fury. On the night of the big carnival, two Germans burst into Johnny's office and demand to see Ballin, and Ballin agrees to meet them in one hour. Superstitious, Gilda portends doom, and later, Obregon warns Johnny of impending trouble. Later that night at the casino, Ballin murders one of the Germans, while at the Mundson house, Gilda seductively dances with Johnny. As they embrace, the door slams and Johnny glimpses Ballin running down the stairs and speeding away in his car. Johnny follows Ballin, who is also pursued by Obregon. As they race onto the beach, Obregon and Johnny see Ballin board a small plane that explodes soon after takeoff. Unknown to them, Ballin has staged the explosion and parachutes from the craft to the safety of a waiting launch. With Ballin's presumed death, Johnny weds Gilda, who has inherited her husband's estate, and assumes control of the cartel. Johnny, who has married Gilda for revenge, refuses to live with her but makes her his captive, assigning his thugs to guard her day and night. One day, a German visits Johnny and asks for the return of the tungsten patents, explaining that the Nazis allowed Ballin to buy the patents as a front and now want them back, but Johnny refuses. Slowly realizing that she is a virtual prisoner, Gilda flees to Montevideo to file for divorce. There she is advised by Tom Langford, an attorney seemingly smitten by her charms, to return to Buenos Aires and file for an annulment instead. Gilda follows his advice, but upon arriving in Buenos Aires, she finds Johnny in her hotel room and realizes that Langford is in his employ. Defeated, Gilda performs a drunken dance of seduction onstage at the casino while Obregon counsels Johnny to turn over the patents to the police and reconcile with Gilda. When Obregon discloses that Gilda's infidelity was only an act to torment Johnny, Johnny contritely approaches her to apologize. Just then, Ballin appears and accuses them of betrayal. As Ballin trains his gun on them, Uncle Pio stabs him in the back with his own walking stick. Obregon magnanimously declares the killing self- defense, thus freeing Gilda and Johnny to leave the country and begin life anew.