En exuberance of high spirits at Prince Orlofsky’s ball. A choir by the guests is followed by Orlofsky’s reckless satiric songs. Among the dancers invited by the prince and the masked guests there’s Adele – in her mistresses elegant dress, and Eisenstein, in the guise of a marquis. Because of the dress, Eisenstein recognizes his wife’s maid, and they agree not to reveal each other’s identities. The prison warden Frank, who is also present, introduces himself to the marquis as a noble chevalier. They become friends. Rosalinde appears. She is dressed as a bat. The enchanted Eisenstein flirts with her, and is forced to present the “bat” with his watch – Rosalinde’s gift to him. A merry choir song, during which Frank and Eisenstein drink to their brotherhood, concludes the ball. The clock strikes twelve. Eisenstein must go to jail. So does Frank.