At a fast food restaurant, a thief attempts to steal a Volkswagen van but is stopped by a robot inside named “BB,” which grabs him by the throat and chokes him. After the robot loosens its grasp, the thief escapes. Later, BB, his owner, Paul Conroy, and his mother, Jeannie, arrive at their new home. As Paul unloads BB from the car, a neighborhood boy named Tom is startled by the robot and crashes his bicycle. Paul reveals he is BB’s inventor and shows Tom the circuit board that is BB’s brain. When Tom says they will probably meet again in high school, Paul responds that he is attending Polytech College on a scholarship to study the human brain. At Polytech, Paul, Jeannie, and BB meet Dr. Johanson, who shows Paul his new computer laboratory. At home, Paul does yard work and BB mows the lawn. Samantha, the girl next door, notices BB, and Paul introduces himself. As they talk, Paul notices bruises on Samantha’s arm. He invites her to his house, but she sees her father, Harry, glaring at her by the side door, and excuses herself. When Paul and BB accompany Tom on his paper route, he learns that Samantha’s father is “a crazy man” as their neighbor, Elvira Parker, who keeps her front gate padlocked because she does not like robots or people, aims her shotgun at the boys until they leave. Down the street, Carl, the neighborhood bully, attempts to attack BB with a can opener. When Paul intervenes, Carl pushes him to the ground. BB grabs Carl’s crotch with his claw-like hand. Carl orders his cronies to retreat on their motorcycles. After the robot relaxes his grip, Carl follows his biker buddies, but vows revenge. Later, Samantha visits and Paul shows her his room and the attic. However, her father arrives at the front door and makes her leave. At night, Samantha has nightmares about her father. In a lecture hall, Paul explains to other students that after trial and error, BB’s brain is very similar to a human brain. One day, Paul, BB, Samantha, and Tom play basketball. When the friends give BB a chance to shoot a basket, he accidentally hurls the basketball onto Mrs. Parker’s porch, and Mrs. Parker confiscates the basketball. At the laboratory, Dr. Johanson is surprised when Paul discovers he can make a cadaver move by hooking it up to BB’s circuit board. As Paul and his mother carve a pumpkin at home, Samantha appears with a nosebleed and claims to have been clumsy but Jeannie suggests Harry is responsible. Samantha is defensive, citing that while her father is not perfect, he is still her father. During Halloween, the friends command BB to open the padlock on Mrs. Parker’s front gate so they can ring her doorbell. When Samantha approaches the front door and rings the bell, an alarm goes off. The friends panic and hide in the bushes. Mrs. Parker appears and destroys BB with her shotgun. When Samantha is a dinner guest one evening, Paul walks her home and gives her a kiss. Samantha searches for her father when she returns. He accuses her of lying about her whereabouts and slaps her. She tumbles down the stairs, and hits her head against a wall. Paul and his mother see an ambulance parked on the street. Harry mutters his daughter was clumsy and fell after slipping on books she left near the stairs. At the hospital, Paul learns Samantha is brain dead and on life support. Paul and Tom drive to the hospital in the van. There, Samantha’s father gives the signal to turn off life support earlier than anticipated. Paul returns to the van with Samantha’s dead body. Soon, Paul implants what is left of BB’s computer brain inside Samantha’s head. He tells Tom it is a little like a pacemaker. If there is any life left in her body, the implant will find it. Paul turns on the control switch, and Samantha’s leg moves by itself. They hide Samantha’s body in the tool shed, where Paul reanimates Samantha’s body, and she sits up. He leaves her but returns later when he hears a noise. He finds Samantha upright and staring through the window at her father next door. She gives Paul a knowing glance. He uses his control switch to be put her in a sleep state. Later, Jeannie complains that Paul has left an expensive sleeping bag in the backyard. He apologizes, then checks the shed and finds Samantha missing. Meanwhile, as Harry goes to the basement, someone pushes him down the stairs. After his fall, he looks up and sees his daughter. She approaches him with her hands outstretched, while he grabs a shovel. She pulls the tool out of his hand. He confesses that he did not mean to kill her. Then, she breaks his hand and hoists him in the air by the throat until she breaks his neck. Paul notices smoke pouring out of the chimney at Samantha’s house. He goes into the basement, and pulls Harry’s partially incinerated body out of the furnace, and hides it in the coal bin. He locks Samantha in a room at his house, and focuses on how he is going to resolve his predicament. Across the street, Mrs. Parker sees Samantha in the window and calls the police. Next, she discovers that someone has removed the padlock from her front gate. A basketball bounces through her dining room, and she grabs her shotgun. Mrs. Parker hears running footsteps and locks herself in the living room. Suddenly, Samantha grabs her and slams her against the wall. She throws the basketball at Mrs. Parker’s head, which explodes upon contact. At night, Paul has nightmares about basketballs and Harry’s burned corpse. He goes to the kitchen and spills a glass of milk when Samantha surprises him. Paul orders Samantha to wait outside when Jeannie comes downstairs, and after his mother goes back to bed, he hides Samantha in the attic. As he looks out the window, he sees paramedics loading Mrs. Parker’s body into an ambulance and suspects the worst. After talking to a neighbor on the street, mother and son discover Harry and Mrs. Parker have been murdered in gruesome ways. The next day, Samantha escapes from the attic, and Jeannie tells her son she heard noises coming from his room. Paul finds Samantha crying and orders her not to wander, then Tom calls and insists he can no longer keep Samantha’s reanimation a secret. Paul asks to meet to talk before Tom goes to the authorities, and takes him to see Samantha in the attic, but he is scared by her robotic presence and runs away. As the boys fight, Jeannie returns and confronts Paul about skipping classes. Tom leaves, threatening to call the police. However, Samantha flies out of an attic window and attacks him on the lawn. When Paul breaks up the fight, Samantha chokes him, but then realizes it is Paul and runs away. As Paul chases after her, biker Carl attacks him. Samantha hoists Carl in the air and throws him onto the hood of a patrol car. Again, Samantha runs away, but soon returns to the tool shed, where Paul explains that Dr. Johanson can help them. They hug, but police surround them with their guns drawn. Samantha cries out for Paul, then charges at an officer. He shoots her in self-defense. Later, Paul sneaks into the morgue, and tells Samantha’s corpse he is going to rescue her. Instead, she reanimates, her human skin peels away to reveal BB underneath, and she strangles him.