In 1955 Vienna,
during its post-war occupation, the black-market dealer Dr. Falke moves freely through the French, British, American and Russian sectors, dealing in champagne and caviar amongst the highest echelons of the allied powers. After a costume party, French Colonel Gabriel Eisenstein plays a practical joke on a drunken Falke, depositing him, asleep and dressed as a bat, in the lap of a patriotic Russian statue, to be discovered the following morning by irate Russian soldiers. Falke is nearly arrested until his friend General Orlofsky of the USSR intervenes. A vengeful Falke plans an elaborate practical joke on his friend, involving Orlofsky, British Major Frank who is sent to escort the French colonel to jail for his misdemeanor, Eisenstein's beautiful wife Rosalinda, her maid Adele and a masked ball where no one is who they seem. Complicating matters is American Captain Alfred Westerman, an old flame of Rosalinda who is determined to take advantage of her husband's absence, deliberately taking the hotel room next to hers. When Major Frank, arriving to take Eisenstein into custody, catches Alfred in Rosalinda's room, in Eisenstein's dressing gown, he takes Alfred to be Eisenstein and arrests him (Alfred) instead. To avoid scandal, Alfred does nothing to disabuse Frank of his error. Later that evening, at the masked ball hosted by Orlofsky, Adele, wearing one of her mistress's gowns, is spotted by Eisenstein, who is unable to do anything about it (as he is supposed already to be in jail and is attending the ball only with the connivance of Orlofsky, at Falke's instigation) and she catches the eye of both Orlofsky and Frank. When the masked Rosalinda arrives, Eisenstein pursues her but she flees with his watch – which Falke slyly tells him will reappear again at his home. At midnight, Eisenstein presents himself at the jail but when he finds Alfred there, still in his (Eisenstein's) dressing gown, he (Eisenstein) realizes that Alfred must have been courting Rosalinda at their hotel, so he rushes back there to confront her, followed by Alfred and Frank, the mistaken identity having been uncovered. She retorts by showing him the watch he had given her at the ball, and he begs forgiveness. All this is overhead by the rest of Orlofsky's party guests (who have all found their way back to the hotel) and Falke admits that he was behind the charade. As all sing and dance, Alfred allows himself to be re-arrested in Eisenstein's place. ==Cast==