In a quiet, small-town high school setting in Southern California, Laura Ramstead, a senior and standout athlete, collapses during a track meet and dies suddenly from a cardiac embolism. Two months pass before her elder sister, Anne, a U.S. Navy officer, returns to town to participate in the upcoming graduation ceremony where Laura is to be honored. Anne carries a heavy suspicion that Laura’s coach, Coach Michaels, pushed Laura too hard, contributing to the tragedy.
As Anne moves through downtown, she glimpses Paula, one of Laura’s teammates, heading toward the woods on jogger’s trails. Paula is soon found murdered, stabbed by an unseen killer. The town begins to sense something ominous is at play. At the high school, Anne attends a graduation rehearsal as a special guest, then visits Laura’s boyfriend Kevin to give him one of Laura’s medals as a memento. Meanwhile, in a different corner of the school’s world, Sally, a gymnast preparing for a photoshoot, is startled in the locker room when her classmates Doris and Joanna enter. Overwhelmed, Sally cannot perform, and the locker-room scene moves toward a chilling moment: a figure dressed in fencing attire arrives and stabs her through the throat with a fencing sword.
The violence continues into the woods the next day when Ralph, another track member, encounters Doris and Joanna. They tease him by tossing his football into the underbrush, but when he searches for it, the killer strikes from the shadows, throwing the ball back with a sharp metal spike that impales him. That evening, a graduation dance unfolds at the high school. Dolores, a flirtatious track teammate, leaves the dance with her boyfriend Tony and the couple heads into the woods for privacy, only to be met by the killer, who decapitates them both with a sword.
Principal Guglione receives anxious calls from the parents of Paula, Sally, Tony, and Dolores, who have vanished. Inspector Halliday arrives to investigate the growing string of disappearances. On the track field, a lone track member, Pete, tries to pole vault, but the pit’s pads are replaced with steel spikes, and Pete is killed on impact. Halliday questions Coach Michaels about the mounting disappearances; Michaels, furious, reveals that he has just been fired due to the media fallout surrounding Laura’s death.
Doris and Joanna discover Sally’s body stuffed inside a locker in the locker room. The screams draw Coach Michaels to the scene, where Kevin also arrives. Kevin accuses Michaels of the killings, and a struggle ensues. Anne and Halliday show up, and Anne spots a photograph of the track team with each face crossed out—except for Kevin’s. Michaels flees into the wooded trails, with Kevin pursuing him, and Anne and Halliday in pursuit as well. The confrontation exposes Ralph’s body and then leads to a final chase where Kevin’s identity as the killer emerges: he has been systematically eliminating teammates to assign blame for Laura’s death.
In a dramatic turn, Halliday shoots Coach Michaels to death, mistakenly believing him to be the perpetrator. The moment after, Anne visits Kevin’s house and discovers Laura’s corpse in Kevin’s bedroom, dressed in a graduation cap and gown. A crazed Kevin bursts in, intending to kill Anne so she won’t “take Laura away.” During their struggle, Anne hurls Kevin and Laura’s corpse through a window. She runs to the high school track field, pursued by Kevin beneath the bleachers. There, she finds Dolores’s severed head and Pete’s spike-riddled body in a storage shed. In a final struggle, Anne pins Kevin to Pete’s spike-lined remains and kills him.
Back at home, Anne gives her statement to the police, but the ordeal continues to haunt her. She returns to an empty house, only to be haunted by a vision of an undead Kevin in her room—though it’s later revealed to be her intoxicated stepfather Ronald. On the morning that follows, a traumatized Anne leaves town by taxi as a Graduation Day banner hangs over the main street, signaling the end of the long, deadly sequence of events that began with Laura’s sudden death and culminated in a brutal, personal reckoning.
