Wealthy Buenos Aires casino owner Ballin Mundsen's best friend is a cane that sheathes a sharp blade. After he uses it to save gambling con man Johnny Farrell from an armed robber, Johnny becomes another best friend by protecting Ballin's casino from cheats like himself. Johnny's only other friend in the casino is bathroom attendant Uncle Pio. As Argentina celebrates Germany's surrender in WWII, Johnny is disappointed when Ballin surprises him with his new wife Gilda. Gilda and Johnny attempt to conceal their previous relationship from Ballin but openly hate each other.
Gilda picks up other men to make Johnny jealous. He conceals her promiscuity from Ballin. Ballin confides in Johnny that he runs a tungsten cartel and plans to rule the world as long as Gilda and Johnny support him. But Gilda's and Johnny's joint attempts to conceal her promiscuity appear suspicious. Gilda and Johnny finally surrender to their desire but are discovered by Ballin. Ballin flees from detective Obregon after murdering a German cartel member. He stages his own death for Obregon.
Johnny marries Gilda and replaces Ballin as head of the cartel. Gilda's happiness at the marriage vanishes when Johnny punishes her prior infidelity by making her faithful to Ballin. Johnny ignores her, prevents her from dating other men and lures her back to Buenos Aires after she runs away. Gilda begs for a divorce but he refuses, so she fights back by performing a striptease at the casino. She's hauled offstage and Johnny hits her. Obregon tells Johnny that Johnny and Gilda love each other. He asks Johnny for the cartel members' names and patents that the German cartel members wanted Ballin to return after WWII. Johnny quickly surrenders what Obregon wants. Obregon tells Johnny that Gilda is going home and her promiscuity was all an act.
Johnny apologises to Gilda and asks her to take him home. Ballin reemerges and threatens to shoot both of them for their infidelity to him but he's killed with his own cane by Uncle Pio. Johnny lies to Obregon that he was the one who killed Ballin, but Obregon says that Ballin's death was justifiable. Gilda and Johnny leave together.