Eisenstein is to report to jail for a minor offence, but his friend, Dr. Falke has secured invitations to Prince Orlofsky’s party that evening. Hoping to enjoy the female company, Eisenstein slips out without telling his wife, Rosalinda who, finding herself free, arranges her own entertainment with her old flame, Alfred, and gives her maid, Adele, the evening off. Adele also obtains a ticket to the party from her sister Ida. The prison warden comes to arrest Eisenstein, finds Alfred making himself at home. The first mistake in identity occurs with Alfred being arrested in Eisenstein’s place.

            The scene shifts to an opulent party at Prince Orlofsky’s palace where Falke tells him of the time Eisenstein embarrassed him by leaving him drunk, asleep, and dressed as a bat in a public park following a costume party. The Bat plans his revenge and the Prince is eager to help. Eisenstein is introduced to the guests as a French marquis. He sees Adele and demands to know what his chambermaid is doing there, but Adele, posing as an actress, puts him in his place for this new mistaken identity. Warden Frank is introduced as a French Chevalier and quickly becomes friends with Eisenstein – each of them recognizing the other as a fake Frenchman but unaware of their true identities. Falke has arranged for Rosalinda to be there but disguised as a countess from Hungary. She is outraged to see her jailbird husband flirting at the party but another mistaken identity occurs when he sets his eye on the Hungarian countess. Rosalinda takes Eisenstein’s pocket watch as evidence. He is trying to retrieve it when the clock strikes 6am, the time he is to report to the prison.

            Frank, still feeling the effects of the party, returns to the jail to find that Alfred (mistaken for Eisenstein) has asked for a lawyer. The guests from the party descend upon the prison, having been let in on the plot by Falke. Eisenstein arrives and identifies himself to Frank who does not believe him. After all, he himself had arrested Eisenstein at home the night before. Eisenstein realizes that Rosalinda had been entertaining a man while he was at Orlofsky’s party. He takes the wig and gown from the arriving lawyer and, in this disguise, wrings a confession from Alfred and Rosalinda before flinging off  the wig and confronting his wife. She, in turn, produces the watch and turns the tables back on her husband. Falke confesses that the whole event was his beautifully-crafted revenge on Eisenstein. The operetta ends with reconciliations all around and the promise of a real stage career for Adele.