
10-year-old Cady, along with her mom and dad, gets into a car accident. Her parents are killed, and the girl is sent to live with her Aunt Gemma, an employee of a corporation that produces technological toys. Not knowing how to cope with the responsibility that suddenly fell on her, and not really wanting to spend time on her niece, Gemma introduces Cady to an experimental android doll M3gan, who has artificial intelligence. The new "girlfriend's" primary task is to protect the child from all sorts of physical and moral harm, and M3gan takes this too literally.