Julie is babysitting at the Hummers' residence when she begins to receive unsettling phone calls from a menacing figure known only as the "Breather." Suddenly, her boyfriend, Charlie, makes a surprise entrance into the house. As they head upstairs to spend some intimate time together, Julie insists that Charlie take a shower first. Unbeknownst to them, the heavy Breather, clad in green rubber gloves and black boots, is stealthily exploring the Hummers' home, ultimately choosing a paper clip as a weapon, which he uses to stabb Julie fatally. When Charlie returns, he is horrified to find that a large green garbage bag has smothered him.
During the funeral for both Julie and Charlie, Principal Peters addresses the attendees, mentioning various events happening that day, from classes to the prom. Among the mourners, Malvert, the janitor, steps forward in his striking green gloves and black boots, prompting Peters to remark on his suspicious demeanor. Nearby, Toby confides in her friend Hardy about her earlier warnings to Julie regarding Charlie. Meanwhile, Joe and Bertha sneak off to have a rendezvous in Joe's car, but their plans are interrupted when the killer ambushes Bertha with a bookend shaped like a wooden horse's head. Joe, oblivious, returns with condoms only to face a gruesome end at the hands of another person draped in a garbage bag.
At Lamab High School, as Mr. Dumpkin highlights the skill of crafting horse head bookends in class, Toby discovers the bloodied bookend at the crime scene and brings it to his attention. Dumpkin, impressed by Toby's wood staining abilities, acknowledges her talent. Later in the girls' locker room, the heavy Breather lurks, watching as the girls undress. In a frightening encounter, Toby escapes from the Breather but instead runs into the peculiar Malvert who seeks help on a crossword puzzle.
The atmosphere thickens during the town parade, where Toby is accompanied by her fellow classmates and teachers. Ralph, while on a float with Dagmar, is enticed to explore the float further, but while he leaves to speak with the driver about speeding, the killer strikes, mercilessly ending Dagmar’s life with an eggplant. Upon Ralph's return, he, too, falls victim to the unseen terror lurking nearby. As the heavy unfolding tragedy continues, Toby's fears grow, leading her to investigate further into the chaotic scene.
In Principal Peters' office, Toby finds herself cornered by Peters, the sheriff, and others who are convinced of her guilt. Peters is dismissive and sends her off for a psychiatric evaluation, only for the phone to ring again with an ominous threat of impending murder at the football game. While awaiting her evaluation, Toby is filled with dread as the killer's next move is revealed.
Back at the game, a series of unsettling and preventable events transpire, culminating in tragic deaths during what was supposed to be a time of joy. As Toby gathers her courage to uncover the truth, she dons a daring outfit for the prom, believing that the answers lie within Peters' office. Unbeknownst to her, a web of deceit spirals tighter as she confides in Malvert to procure the keys necessary for her investigation.
Amidst confusion and increasing tensions, the prom proceeds. However, when it comes time to crown the prom queen, only one candidate remains standing among the deceased. As the night escalates into a horror show, Toby makes her desperate bid for survival, racing against the clock as Peters' true nature surfaces amidst objections and chaos.
In the end, what begins as a dreamlike hospital recovery quickly morphs into a nightmarish twist of betrayal, as Toby discovers her love interest, Hardy, concealing deadly intentions. Their naive romance veers toward tragedy, culminating with a chilling climax at Toby's own funeral. When she reaches out from the grave, the horror of her fate lingers as a testament to the hidden darkness in those around her.
