Inside a decrepit old building, four children engage in a chilling game where one of them searches for the others while ominously chanting, “the killer is coming!” As they play, Kim and her twin siblings, Alex and Robin, pass by the scene. While Kim and Alex eventually leave, Robin hesitates, eager to join the fun. However, upon entering the building, she is cornered by the others who mercilessly chant "kill!" until she has nowhere left to retreat. Panicked, Robin backs up and tragically falls through a window, plummeting to her death. Concerned for their future, Nick suggests seeking help, but Wendy persuades the group to keep silent about the incident, leading Jude and Kelly to also vow secrecy. They leave the building, riding their bicycles away while an unseen figure watches them depart.
Later that evening, Robin's father, Mr. Hammond, along with the police, examines the scene. They suspect that Robin was murdered by a crazed maniac. As the investigation unfolds, they think they have a lead and go off to question a suspect.
Fast forward six years...
Now adults, Kim ([Jamie Lee Curtis]) and Alex ([Michael Tough]) visit their sister’s grave along with their parents. Suddenly, a mysterious voice begins calling each member of the group that kept the secret, threatening, “I’ll see you at the prom!”, instigating fear in the timid Kelly, while Jude and Wendy dismiss it as a prank. Unbeknownst to them, a dangerous criminal named Leonard Murch has escaped from a nearby mental institution. Detective McBride, Nick's father, is deeply unsettled by the news since Murch, previously deemed mentally unfit to stand trial for Robin's death, poses a significant threat.
That night, as the dance approaches, Nick begins to date Kim, much to Wendy's displeasure, who plots to sabotage their relationship. It’s revealed that Lou, the school bully ([David Mucci]), has a troubling interaction with Kim, for which Alex steps in to defend her. Meanwhile, Wendy’s manipulative schemes intensify.
As the senior prom night finally arrives, excitement fills the air. Mr. Hammond is the chaperone, and Alex is the DJ, setting the stage for a night of festivities. However, beneath the surface of fun, dark events begin to unfold. In the locker room, a masked figure stealthily approaches Kelly after a confrontation with her boyfriend and brutally takes her life.
Simultaneously, Jude and Slick attempt to sneak out for a moment of intimacy, only to fall victim to the same cruel killer. After a series of chaotic events, Wendy experiences her own terrifying ordeal as she realizes someone is stalking her, leading to a heart-pounding chase that ends in her grim fate.
As tensions rise, Detective McBride learns that Murch has been recaptured just as chaos erupts at the dance. Amid the celebration, the atmosphere turns deadly when Lou meets his demise at the hands of the killer, leading to sheer pandemonium as students flee in horror.
In the climax of despair, Kim discovers that the killer is none other than Alex, her own brother, revealing the twisted truth that he believes Kim and her friends were responsible for the death of Robin. As she cradles her wounded brother, Nick arrives only to be engulfed in a heart-wrenching moment as the past catches up with them, leading to a tragic conclusion that will forever alter their lives.
