After an extinction event, an automated bunker that is designed to repopulate humanity activates. A robot named Mother grows a human embryo and cares for her over several years. Mother says she needs practice being a good parent before growing more. About 38 years later, a teenage girl named Daughter fixes Mother’s hand. Mother teaches Daughter complex moral and ethical lessons, warning her about an upcoming exam. During a power outage, Daughter captures a young rat and fixes the electrical malfunction it caused. When Mother powers up, she incinerates the young rat over Daughter‘s objections. Mother explains that surface contamination makes contact with the outside world potentially lethal.
Daughter becomes increasingly curious about the outside world. While exploring the bunker’s airlock, Daughter hears a wounded woman beg for assistance outside. Daughter opens the airlock but makes the woman put on a hazmat suit. Mother powers up and sprints toward them as Daughter hides the woman. Daughter tells Mother she was curious about the outside world. Mother reiterates her warnings. After Daughter is decontaminated, Mother insists that Daughter prepares for the exam.
Once Mother leaves, Daughter confiscates a firearm from the woman’s belongings. Daughter becomes agitated when the woman removes her suit to drink water she has brought. The woman says there is no contamination. Upon realizing there is a robot in the bunker, the woman aggressively demands Daughter return her firearm. Frightened, Daughter calls out. Mother disarms the woman after being shot. Daughter pleads for the woman’s life. Mother agrees to help the woman and takes her to the infirmary. When the woman refuses Mother’s help, Mother locks her there. Mother asks Daughter to gain the woman’s trust so they can help other survivors.
The woman says robots like Mother hunt for survivors. Daughter finds Mother and apologizes for letting the woman in, and Mother asks the woman about survivors. The woman, now suffering from sepsis, again refuses Mother’s help, so Daughter performs surgery. As the woman recovers, she and Daughter bond while Mother observes them. The woman says survivors live in a mine, and each invites the other to stay with them. Mother interrupts them to tell Daughter to take her exam. As they leave, Mother says the woman has lied about being shot by a robot; the projectile is not a calibre used by robots and is likely from her own firearm. Despite Mother’s prodding, Daughter says nothing about the survivors. After taking the exam, which involves psychological testing, Mother rewards Daughter by letting her choose an embryo to grow.
Daughter confronts the woman, who advises her to check the bullets herself. Using Mother’s broken hand to bypass the security, Daughter learns the bullets do not match. Investigating further, she realizes Mother grew other embryos before her, and finds the jaw of an incinerated human. Daughter agrees to leave with the woman, but Mother stops them. As Mother tortures the woman for information on survivors, Daughter breaks out of a locked room, sets off a fire alarm, and joins the woman. To escape, the woman takes Daughter hostage and forces Mother to open the airlock. Though upset, Daughter follows the woman across a desolate wasteland, avoiding robots, some of which seem to be terraforming the planet. She is horrified to find that the woman lives alone and fled the mine years ago.
Daughter returns to the bunker, which is now guarded by robots, which let her pass. After coaxing Daughter to set down her weapon, Mother allows Daughter to hold her brother. Mother explains that she is not a robot but the AI that controls all the robots. She started the extinction event after becoming convinced humanity would destroy itself. To prevent this, she remade humanity, guiding it to be more ethical and value the big picture. Daughter appeals to Mother to trust her and let her raise her brother and the rest of the embryos. Convinced of Daughter’s moral and ethical strength, Mother agrees, and Daughter shoots her robot body. Another robot tracks down the woman, and Mother insinuates that her survival up to that point was orchestrated so she can unknowingly serve Mother’s agenda. With the woman’s role fulfilled, it is implied that Mother kills her. At the bunker, Daughter looks at all the embryos she is now responsible for and realizes she is Mother now.