In the bedroom of their wealthy Madame, Claire, a maid, chastises in an exaggerated tone her older sister. Claire makes herself up at the dressing table and calls in Solange to prepare her dress and accessories. She accuses Solange of letting the milkman (Mario) seduce her, and insults her appearance and manners. Claire defends herself for having "denounced" Monsieur to the police in a letter that sent him to prison.
Claire submits to a red dress and says Solange loathes her. Claire kicks Solange in the temple. When Solange's and Claire's fingers accidentally touch, Claire says she cannot stand touching her. Solange reprimands her and speaks of the importance of boundaries and frontiers between them. Solange asks if Claire is ready, and then declares her hatred for Claire and insults her aristocratic appearance and behavior. Solange shows her in the mirror the two maids. She tells her to despise them, then says "We're merged in our hatred of you." Claire tells her to get out, and Solange says she will return to her dirty kitchen, but first she will "finish the job."
Claire urges Solange to help her out of the dress, as Madame will be back. Solange blames Claire for never being ready and allowing Solange to finish her off. Solange says Claire started their fighting by bringing up Mario and mingling her insults with details from their private lives. Claire says she envies Solange for having seen Madame's crestfallen face when she heard of her husband's arrest. She takes credit, however, for having written the anonymous letter that sent him to prison.
Solange says nobody loves them, but Claire insists that their kind Madame does. Claire tells her to calm down and says she has some information on Solange that she would not want revealed. Claire brings up the fantastical stories she has written that Solange used as escapism, such as the one in which she vicariously fled France with her thieving husband. Claire says the reason she hates Solange is because in her attempt to kill Madame, she was aiming for Claire.
Claire answers the phone and learns from Monsieur that he has been freed from prison on bail. Solange tries to calm down Claire. Claire says it is her turn to dominate Solange, and gives her a number of household orders. Solange fantasizes about how they will kill Madame. The doorbell rings. Claire and Solange scramble to prepare for Madame's entrance. Solange says they need to put ten pills in her tea, and Claire agrees to do it. They both leave the bedroom, and Solange returns with Madame. Madame accuses Solange of pampering her like an invalid. She apologizes, then calls herself old, and says she is thinking of going into mourning. Solange promises never to abandon her. Madame says she is through with her excessive life.
Claire enters with the tea. Madame says the sisters will inherit her lavish lifestyle. She gives Claire the red dress Claire previously wore, and gives Solange a fur cape. Madame spots the telephone off the hook. Claire says it was Monsieur. After Madame presses, Solange says they wanted to keep it as a surprise—Monsieur is free and waiting for her at a bar. In a flurry, Madame orders Solange to get her a taxi and Claire to get her furs ready. Madame is piqued by the mystery of the letters, Solange's delay, and the sisters' not telling her Monsieur had called. Claire insists that Madame drink the tea, but Solange runs in, pushes Claire aside, and says the taxi is finally ready.
Solange tries to stir her sister into a rage, telling her that Madame and Monsieur will probably find out about the letters. She loathes Madame and criticizes her gifts, including the fur, which she took back. Claire angrily asks if Solange wants to "make a scene." Solange praises Claire's beauty, but Claire tells her to start with the insults. She is unable to do it, so Claire takes the reins and tells her how much she despises servants.
Solange takes over and, with a riding whip, orders Claire down on her knees. Claire reluctantly does so, and Solange slanders her more, strikes her, and commands her to lie down. Solange tells her to go into the kitchen, and Claire screams for help. Solange tells Claire that she performed abortions on herself to keep Claire alive. Claire runs around the room, and Solange chases her, but when Claire gags and says she feels ill, Solange comforts her and walks her off to the kitchen, where she has ways of "putting an end to all suffering."
Solange returns from the kitchen, wearing her black dress. In her ensuing monologue, she addresses imaginary characters on stage. She celebrates having strangled Madame with the dish-gloves. She imitates Madame's voice and complains about having to wear mourning for her maid. In her own voice, Solange says Madame should not pity her, as she's her equal. She addresses a police inspector, telling him Monsieur used to obey their orders when they threatened him. She says she has been a good servant, but now she has strangled her sister. Solange smokes a cigarette, coughs, and goes out on to the balcony, her back to the audience. She imagines the hangman taking her away. She sees herself being led by all the maids in the neighborhood for Claire's funeral procession.
Claire, visible only to the audience, leans against the kitchen door and listens to her sister. Returning to the room, Solange cries for poor Claire. Claire enters the room, wearing the white dress. Claire says for "Claire" to pour her a cup of tea. Solange protests and tiredly sits down, but Claire insists. She tells "Claire" to stand up straight and to "represent" her in the world. She lifts Solange up and makes her repeat after her "Madame must have her tea" and other corresponding sentences. Solange brings in the tea and Claire drinks it. She comments on the end of the theatrical production—the orchestra plays, the attendant raises the red velvet curtain, and Madame descends the stairs and gets into her car with Monsieur. She is dead, but rings the bell, enters the apartment, and finds Madame dead. Her two maids are alive, however, risen up from Madame's form, now free. Solange proclaims themselves, "beautiful, joyous, drunk, and free!"