Vienna. The Marschallin, Princess von Werdenberg, and the young Octavian, Count Rofrano, rise regretfully from her bed, where they have spent the night. At a sound in the hallway – perhaps the Marschallin’s husband – Octavian hides and disguises himself as a chambermaid. The Marschallin’s cousin, Baron Ochs auf Lerchenau, enters asking her whether she has given thought to his letter, in which he asked her to choose a Rosenkavalier – Knight of the Rose – to take the customary silver symbol to the woman Ochs has decided to marry, Sophie, the daughter of the very wealthy and recently ennobled Herr von Faninal. She suggests Octavian and shows Ochs his picture. Ochs cannot help but see the resemblance to “Mariandel,” the maid, whom he shamelessly pursues.

The Marschallin holds her morning levée, during which she is addressed by an animal vendor, a milliner, three noble orphans, and two Italian scandalmongers, and sung to by an Italian tenor. Ochs browbeats the notary into drawing up a marriage contract. Losing his temper, he interrupts the tenor’s song. The Marschallin sends everyone away, but not before Ochs has left her with the silver rose – and engaged the intriguers, Valzacchi and Annina, to secure him an assignation with “Mariandel.” The Marschallin muses on the passing of time.

Octavian returns, dressed as himself, and notes the Marschallin’s melancholy mood. She assures him he will leave her for a younger woman. He naturally protests, and she sends him away. When she realizes they have parted without a goodbye kiss, she sends her footman after him, but he has already ridden away. She calls her page to take the rose to him.

Faninal’s salon. Sophie waits excitedly with her duenna, Marianne. Octavian brings the rose to Sophie and both are smitten. The real suitor enters and Sophie is appalled by the Baron’s rude manners. Ochs goes into an adjoining room with the notary and Sophie and Octavian agree that she must not marry Ochs. As they move to embrace, they are caught by Valzacchi and Annina, who call for the Baron. Octavian challenges him to a duel and wounds him lightly on the arm, at which Ochs shouts bloody murder.

He is cheered when left to rest with a bandage and Faninal’s wine. Annina returns with a note inviting him to a rendezvous with “Mariandel” that evening. He accepts with delight but does not tip her.

A room in an inn. Octavian, now helped by Annina and Valzacchi, sets a stageworthy scene for the confounding of Ochs. The Baron and “Mariandel” soon meet for a private supper, but strange figures appear from trap doors and windows, making Ochs think he sees ghosts. Suddenly a woman dressed in mourning bursts from a blind window, claiming to be Ochs’s deserted wife. It is Annina in disguise, followed by a herd of children screaming, “Papa!” The innkeeper and servants rush in. Finally Ochs calls the police, and claims that “Mariandel” is his fiancée Sophie. Faninal arrives, furious, and sends for the real Sophie. At the height of the confusion, the Marschallin appears. The Police Commissary recognizes her – he was once her husband’s orderly–and she easily explains that this was all a farce. She insists that Ochs leave Vienna, and he does, pursued by Annina and the children, the innkeeper, and his creditors. Now the Marschallin is left with undecided Octavian and anxious Sophie. The day she predicted has come. Quietly she leaves them alone together.