Lisa Harris, Tammy Lauren, is a popular high school student who'd rather spend time with her boyfriend Louis Patrick O'Bryan than focus on her grades. When her classmate Kim Fielding, Shawnee Smith, invites Lisa to dinner at her house, Lisa agrees mainly to see Louis, while Kim has to babysit her younger sister Julia Fielding, Candace Cameron Bure, because their father, Mark Fielding, Alan Fudge, is out of town for the night. The evening takes a turn toward boredom and impulse as the two girls decide to pass the time with prank calls, and Lisa reluctantly participates in the mischief.
Their boredom leads to a chilling game. During one prank, Lisa calls Adrian Lancer, Robert Carradine, a man whose mind seems unsteady after a recent murder—the result of him killing his girlfriend Robyn Griffin, Jo Anderson, who had rejected his proposal. Lisa, trying to end the call, hangs up, but the seeds of danger have already been sown. She and Kim exchange a taunting line as they continue to dial around, and Lisa coldly remarks, I know what you did, and I know who you are as part of the taunting game, a line that will echo with consequences later.
Kim, thinking she’s found a chance at romance with an older man who might appreciate her, agrees to meet Adrian again after Lisa’s provocation. The plan intensifies when Kim actually drives by Adrian’s house, despite lingering nerves about acknowledging who she is to him. Meanwhile, Adrian’s visiting brother Stephen, David Carradine, grows suspicious of Adrian’s strange behavior and the hints of violence tied to his past. The film threads these tensions together as Kim’s nerves tighten and Lisa’s prank spirals out of control, pulling both girls deeper into Adrian’s dangerous orbit.
As events unfold, Adrian confronts Kim when she stops at his door to explain her car trouble, and she pretends to call for help to avoid naming herself. The deception unsettles Adrian, who already suspects who she is, and Kim quickly leaves, forgetting her purse in the process while Stephen reappears to warn Adrian that he’s heard enough. Back at Kim’s house, Lisa’s boyfriend Louis and his friends eventually arrive and expect to take Lisa home, but she refuses to abandon Kim, choosing to stay with her friend instead. The night escalates when Stephen reveals to Adrian that he knows what happened to Robyn, and Adrian knocks Stephen out to keep his secret safe, planning to silence Kim as well.
The tension snaps into action when a police intervention interrupts Adrian’s pursuit. He is chased by an officer who recognizes him, crashes his car, and appears to perish in the explosion—yet his rampage continues toward Kim’s home. Inside the house, Kim confronts the danger and realizes the deadly stakes behind the prank. The fight spills outside, and the family’s dog charges into Adrian, knocking him into a fire that engulfs him. A neighbor, Randy Robert Winley, helps the girls escape just in time, and the incident ends with Adrian burning alive as he fails to hurt anyone else.
In the aftermath, a lingering sense of dread remains. The closing moment stings with a chilling postscript: later, Stephen calls Kim and coldly states, "Kim, I know who you are. You killed my brother," a line that leaves the audience with a haunting reminder of the night’s consequences.
