The film was known as 8 femmes to distinguish it from the 1972 play entitled Huit femmes.
The scene opens with Suzon returning from school for Christmas break, finding her mother Gaby, her younger sister Catherine, and her wheelchair-bound grandmother Mamy in the living room, where most of the action of the film takes place. Their conversation drifts to the subject of the patriarch of the family, and Catherine leads the first song of the film, "Papa t'es plus dans le coup" (roughly, "Dad, you're out of touch"). The singing wakes up Suzon and Catherine's aunt Augustine, who picks arguments with the rest of the family and the two servants (Madame Chanel and Louise), eventually returning upstairs, threatening to commit suicide. Mamy jumps out of her wheelchair, trying to stop her, haphazardly explaining her ability to walk as a "Christmas miracle."
Augustine is eventually calmed down, and she sings her song of longing, "Message personnel" (Personal Message).
The maid takes the tray upstairs, finds Marcel's stabbed body, and screams. Catherine goes up to see what happened and locks the door. The others go finally up to Marcel's room to see him stabbed in the back. Catherine tells the others that they should not disturb the room until the police arrive. Realising that the dogs have not barked the night before, it seems clear that the murderer was one of the women in the house. Attempting to call the authorities, they find that the phone is disconnected, and they will have to go in person to the police station. However, the women are distracted by the announcement that someone is roaming in the garden, who for some reason, the guard dogs are not chasing. The person turns out to be Marcel's sister Pierrette, a nightclub singer who is also rumoured to be a streetwalker, and has not been allowed to the house before, due to Gaby's dislike for her. When questioned, she claims she received a mysterious phone call, telling her that her brother was dead; she also sings "A quoi sert de vivre libre" (What cost living free?), commenting on her sexual freedom.
It is realised that she has been to the house before, as the dogs did not bark, making her the eighth potential killer. The women try to start the car, and find that it has been sabotaged, cutting them off from help overnight, until they can hitchhike to town in the morning. The women spend their time trying to find the murderer amongst them. It is discovered that Suzon in fact returned the night before, to tell her father in secret that she was pregnant. She sings a song to Catherine, "Mon Amour, Mon Ami" (My Lover, My Friend), about her lover, who, is in fact, her father. We later find out that, unknown to everyone involved excluding Gaby, Suzon is not his child, and is actually the child of Gaby's first great love. Gaby reveals that he was killed not long after her conception and that every time she looks at Suzon, she is reminded of her love for him.
Suspicion then swings to Madame Chanel, the housekeeper, whose actions the night before seem suspicious; it is revealed that she has been having an affair with Pierrette, who went to see her brother that night to ask for money to pay off her debts. When some members of the family react in outrage to the fact that she is a Sapphist, she retreats to the kitchen, and sings "Pour ne pas vivre seul" (So as to not live alone).
The spotlight moves to Louise, the maid, who is found out to be Marcel's mistress, yet declares her love for Gaby, yet expresses disappointment in her for her weakness and indecision. She sings "Pile ou Face" (literally Heads or Tails, but referring to the Ups and Downs of life), and removes the symbols of her servitude, her maid's cap and apron, asserting herself as an equal to the other women.
Gaby sings "Toi Jamais" (Never You), about Marcel, saying that he never paid enough attention to her, while other men did; it is revealed that she had an affair with his business partner, the same man who has been having an affair with Pierrette. The two women get into a fight, which turns into a make-out session on the living room floor, which the others walk in on.
Eventually, Madame Chanel decides to reveal the solution to the mystery, but Catherine takes the lead, revealing that she had hidden in her father's closet, and had seen the other women all talk to Marcel the night before, and explains the mystery: Marcel had faked his own death, with her help, to see what was really going on in his house. She claims that he is now free of the other women's clutches, and rushes into his bedroom, only to see him shoot himself in the head, in absolute despair. Mamy ends the film with the song "Il n'y a pas d'amour heureux" (There is no happy love).