Act 1

Paris. 10 August 1792, the day of the capture of the Tuileries during the French Revolution

There is a squabble in the laundry of Caterina Hubscher, a beautiful Alsacian girl, a very free and easy-mannered woman whom everyone calls "Madame Sans-Gêne" (Madame Carefree). One of her customers is Fouché (later Minister of Police under Napoleon), whom Caterina dislikes; another, a quiet young officer who lives nearby, is Napoleon himself. As Caterina is about to close her laundry, a wounded Austrian officer arrives and asks for her help, Caterina hides him in her room. The officer turns out to be the Count of Neipperg. Sergeant Lefebvre, Caterina's fiancé, arrives with more soldiers and is suspicious when he sees the doors closed. He discovers Neipperg but tells his men that there is no one in the room, and to leave. Once alone with Caterina, he helps her to assist the Count.

Act 2

The castle of Compiègne. September 1811

Napoléon is at the height of his career. Lefebvre has distinguished himself in many battles, and has become a Marshal of France. For his success in the siege of Danzig, Napoléon has made him Duke of Danzig. Caterina, the former laundress, is his wife of many years, and now a duchess, but her demeanor has not changed and causes scandals in court. The Emperor orders Lefebvre to divorce Caterina and find a more suitable wife. Lefebvre and Caterina are desperate and also worried about their friend Neipperg, who is suspected by the Emperor of an affair with the Empress Marie-Louise. During a reception, Caterina makes a series of gaffes and gets into a fight with the Emperor's sisters, and the butler announces that the Emperor wishes to see her.

Act 3

Napoléon orders Caterina to divorce her husband and to retire from a life that is not suitable for her. Caterina, however, reminisces about the days when she was a laundress, and he only a young officer, and he is moved even though she also reminds him that he still owes her 60 francs for washing. Then Count Neipperg is caught entering the Empress's chambers. Napoléon is furious. He degrades Neipperg from an officer to a common soldier, and orders his immediate execution. Caterina intervenes: she reveals that Neipperg is innocent and he is forgiven. To the astonishment of everyone, the Duchess of Danzig appears in the salon on the arm of the Emperor, to engage in a hunt.