Businessman Oliver Pope is driving home from work, distracted by a coworker who he believes is trying to steal his position. Distracted, Oliver hits a paperboy riding on a bicycle and knocks the kid to the curb. Oliver stops and gets out, but then turns around and leaves. As he goes, a woman, Muriel Hastings, sees him from a distance and yells at him to stop, but Oliver drives off.
Back at home, Oliver parks the car in the garage. When he comes in, his wife Lillian wonders why he did and says that they were going out. Oliver claims that he's feeling sick and complains about Pete Radcliff, the co-worker who is trying to steal his job. When Lillian disagrees, Oliver snaps at her. As he lies down on the sofa, Lillian notices the headlights of the car through the garage door, flickering on and off. Oliver goes out to investigate and discovers that the car has started up on its own. He turns off the car and goes back inside, and tells his wife that the car must have faulty wiring. She points out that they just had it checked, and then asks if Oliver saw the paper outside.
That night, Oliver secretly calls the hospital and asks about the boy, and is informed that he's in intensive car. He then goes to bed, but he and Lillian are woken up when the car horn keeps going off. He finally opens the hood and yanks out the cables. However, the hood slams down, just missing Henry's hands.
The next morning, Lillian reads a newspaper article about the hit-and-run incident and hopes that the man who did it gets what he deserves. The newspaper article contains Muriel's statement that she saw a man drive off. Oliver says he won't be going in, and the car horn goes off again. Lillian drives it to the garage, but it stops in the middle of an intersection. She returns home and tells Oliver about the incident, and the fact that the intersection was where the paperboy was hit. Lillian had the garage tow it to their place to do the work. However, the car horn goes off and the couple is surprised to discover that the car is back in the garage. They call the garage owner, who thought that Oliver had already picked it up.
Pete stops by the house to tell Oliver that he took care of the work stacking up in his in-box. Offended, Oliver tells him to stop trying to steal his job. Pete snaps back, and then admits that he's on edge because the paperboy was a friend of his kids. When Lillian asks how the paperboy is doing, Pete informs her that he died an hour ago.
A motorcycle policeman, figuring that the hit-and-run driver will return to the intersection, stands watch with Muriel. She finally picks out a passing car as the one she saw hit the boy. The policeman pulls the driver over and confirms that it's Pete.
The next day, a satisfied Oliver reads about Pete's arrest. Lillian doesn't believe he did it, and Oliver smugly tells her that he said Pete was sneaky. He's also satisfied that Pete doesn't pose a threat to him anymore, although he hastily denies it when Lillian accuses him of thinking just that. As they talk, Lillian hears a noise from the garage. Oliver doesn't want to go near the car, but he relents when Lillian say she's going to call the police. He goes into the garage and the front fender falls off of the car, which then starts up. Panicking, Oliver runs back into the kitchen.
That night, the Popes are trying to sleep when loud music starts playing outside their bedroom window. They assume it's the neighbors and Oliver goes out through the garage to talk to them. He discovers that the music is coming from the car. The radio switches to a newscast about the dead paperboy and Pete's arrest. Oliver turns off the radio but it starts up again, playing the same newscast. He finally smashes the radio and then the flashing headlights. When he starts to leave, the horn goes off and he opens the hood to smash that as well.
The next day, Oliver prepares for work and claims that he's feeling better. He assures Lillian that he'll put a lock on the garage to keep the prowlers out. As Oliver goes, he tells Lillian that he's going to walk because he plans to sell the car and is glad to be rid of it. As he walks to the bus, Lillian is surprised to see the garage door open and the car pull out on its own. It drives down the street, following Oliver. He soon starts to run, but slips on the wet concrete. The car screeches to a halt inches from his head and the passenger door opens. Realizing that there's no escape, Oliver gets in and the car drives him to the police station and then opens the door so he can get out and confess his crime.