Johnny McFarley, the local 12-year-old paperboy, arrives at elderly Mrs. Thorpe's home and smothers the woman with a plastic bag.
The movie then cuts to Melissa, a teacher making concluding remarks to her seventh grade English class. When Melissa returns home, she receives a phone call from her friend, Diana, who tells her that her mother has died. Melissa and her daughter, Cammie, travel back to Melissa's hometown for her mother's funeral. Once Melissa and Cammie arrive at the late Mrs. Thorpe's home, they are greeted by an enthusiastic Johnny who kindly offers to take their luggage inside. Johnny asks permission to join them at the funeral. During the limousine ride to the funeral, Johnny reveals that his mother is dead and that his father, a sales representative, is rarely around because of the nature of his job.
After the funeral, Johnny sneaks into the Thorpe house and places a baby monitor in the vent so he can eavesdrop. Later, Melissa invites Johnny to a barbecue that she and Cammie are having in which Johnny accepts under the condition that he is allowed to cook. Johnny takes video of the BBQ while he waits for Melissa, only to discover that she is going on a date with her boyfriend, Brian. When Brenda arrives to babysit Cammie, Johnny reacts violently by smashing a barbecue plate and then retreats to his home.
Later that night, Johnny walks back to Melissa's house with a letter of apology only to stumble upon Brenda making out with her boyfriend. Brenda catches him and, the next morning, tells Melissa that Johnny has been spying on her. Johnny seeks revenge by tampering with the antenna that Brenda uses to sneak into her bedroom window. Successful in his scheme, Brenda falls and injures herself. Johnny later explains casually to Melissa that Brenda is now paraplegic.
When Johnny takes Cammie along to collect money from his paper route, he tells her that one of his customers, Mrs. Rosemont, is a witch. When Johnny walks away from Cammie to retrieve his money from the mailbox, Mrs. Rosemont warns Cammie that Johnny has the Mark of Cain and that she should stay away from him. Later, Cammie tells her mother what was revealed to her when she was with Johnny collecting money. Concerned, Melissa confronts Mrs. Rosemont.
Johnny sneaks into Melissa's house in order to make an apple pie. Melissa is not pleased about this. Later that night, Johnny, along with his father, apologizes for his actions. Melissa tells Johnny that he cannot come to the house unless he is invited. She then tells his father that he should spend more time with him. Johnny's father gives his son a set of golf clubs as an apology for not being there for him, and tells Johnny that they will be spending much more time together in California because of a recent promotion. Fearing that he will not see what he considers to be "his family" again, Johnny kills his father with a fold-out putter.
Soon, Melissa goes to Mrs. Rosemont where it is explained that Johnny was emotionally and physically abused by his mother and that he murdered her. When Johnny finds out about their conversation (owing to his eavesdropping device), Johnny grows angry and rides his bike to Mrs. Rosemont's house. He snatches her inhaler and leads her to believe that he killed her dog - he actually smashed ketchup bottles while the dog was in a different room completely fine. Mrs Rosemont then has a fatal heart attack.
Johnny then goes to Brian's workplace, knocks him out, and sets it on fire. Brian manages to regain consciousness fast enough to escape. Johnny then calls Melissa and tells her to come to his house. Melissa denies Johnny's request until she hears Cammie calling her name. Johnny's true intentions are finally unveiled when he reveals that he killed Melissa's mother to lure them to the house in hopes of starting a new family. Melissa frantically searches Johnny's house wherever she hears Cammie's voice only to find that the sound has been coming from Johnny's home movie and the baby monitor in the basement. As Melissa incessantly refuses to be Johnny's mother, an angry Johnny then tries to bury Melissa in a hole created for his father, only to have her escape through the window.
Armed with a pickaxe, Johnny pursues Melissa, who is carrying Cammie as she is running. Melissa soon wears out and tells Cammie to run. Johnny and Melissa struggle with the pickaxe until the police arrive. Johnny tries to use this to his advantage, frantically lying, saying Melissa is crazy and tried to kill him. Johnny then sees Brian step out of the squad car, saying that it's over. The cops take a hysterical Johnny away as he begs for Melissa to tell them he is innocent as the film ends.Marc Marut as Johnny McFarley
Alexandra Paul as Melissa Thorpe
William Katt as Brian
Karyn Dwyer as Brenda
Krista Errickson as Diana
Frances Bay as Mrs. Rosemont
Brigid Tierney as Cammie Thorpe
Barry Flatman as Mr. McFarley
Derek Johnston as Brenda's Boyfriend
Claire Riley as Jeanne Stalcup
Bobo Vian as Dora
James Rae as Travis
Sam Stone (uncredited) as Police Sergeant