In 1970, Cleo is a maid in the Colonia Roma neighborhood of Mexico City working in the household of Sofia, whose occupants also consist of Sofia’s husband Antonio, their four young children, Sofia’s mother Teresa, and another maid, Adela. Antonio, a doctor, leaves for a conference in Quebec, Canada. Among scenes of Cleo’s life with the family – her cleaning, cooking, taking the kids to and from school, serving them meals, putting the kids to bed and waking them up – it becomes clear that Sofia and Antonio’s marriage is strained. After a brief return, Antonio leaves again, saying he is going to Quebec for a few weeks.
In their time off, Cleo and Adela go out with their boyfriends, Fermín and Ramón, to the theater. At the entrance, Cleo and Fermín decide to rent a room instead of seeing the movie. Fermín shows off his martial arts skill using the shower curtain rod as a pole. At another date, both couples meet in a movie theater, where Cleo tells Fermín that she thinks she is pregnant. As the movie (La Grande Vadrouille) is about to end, Fermín says he is going to the bathroom and will be back, but then does not return and is nowhere to be found when Cleo goes outside. Cleo reveals the same concern to Sofia, who takes her to get checked at the hospital where Antonio works. The doctor there confirms her pregnancy.
Sofia takes Cleo, Adela, and her children to a family friend’s hacienda for New Year’s. Both the landowners and the workers mention recent tensions over land in the area. During the celebrations, a fire erupts in the forest. Everyone helps put out the fire as a man counts down the remaining seconds of 1970 before singing a Norwegian lullaby in the foreground.
Back in the city, Cleo accompanies the children and their grandmother to a movie theater to watch Marooned. As they are entering, Antonio is seen rushing out with a young woman. Sofia tries to hide Antonio’s departure from the children, but her second son learns of it by eavesdropping in on a phone conversation. She asks him to not tell his other siblings who believe their father is still away on business in Canada.
Through Adela’s boyfriend, Cleo finds Fermín at an outdoor martial arts training class, but he refuses to acknowledge that the baby is his and threatens to beat her and their child if they ever come to look for him again.
Cleo is now nearing her due date. Teresa takes her shopping for a crib. On their way to the store, they observe students gathering to protest in the streets. As they are browsing upstairs in the furniture store, the protestsbelow turn murderous between police clubbings, while bands of roving youths, implied to be the paramilitary group Los Halcones (The Hawks), randomly shoot at protesters. When a wounded man and a woman run into the store trying to hide, several youths find the man and kill him with a gunshot as the shop patrons take cover. Another gunman pointing a gun at Cleo turns out to be Fermín, who glares momentarily before running off with the other youths. Just then, Cleo’s water breaks.
Cleo, Teresa, and their driver try to get to the hospital quickly but are impeded by violence in the streets and car traffic. Cleo is taken into the delivery room. Antonio comes by to reassure her, but makes an excuse to avoid staying with her. The doctors hear no heartbeat in Cleo’s womb and take her into surgery, where they deliver a stillborn baby girl. Multiple attempts to resuscitate the infant fail. The doctors give the body to Cleo for a few moments before taking it away.
After a drunken attempt to park the family Ford Galaxie in the narrow garage area, Sofia buys a narrower Renault car, but plans a final trip in the Galaxie for a family holiday to the beaches at Tuxpan, taking Cleo to help her cope with her loss. Sofia tells the children over dinner that she and their father are separated and that the trip was made so their father can collect his belongings from their home. At the beach, the two middle children are almost carried off by the strong current until Cleo wades into the ocean to save them from drowning even though she herself does not know how to swim. As Sofia and the children affirm their love for Cleo for such selfless devotion, she breaks down and reveals that she had not wanted her baby girl to be born. They return to their house, with the bookshelves gone and various bedrooms reassigned. Cleo prepares a load of washing, telling Adela she has much to tell her, and suggests she skip the flirting as a plane flies overhead.