In 1957, Hamilton High School prom queen Mary Lou Maloney dies a fiery death during the prom when her rejected boyfriend, Bill Nordham, plays a cruel prank using a trunk filled with fire-retardant chemicals that tragically ignites. Thirty years later, in 1987, Bill is now the high
school principal, and his son, Craig, is dating the modern prom queen hopeful, Vicki Carpenter. During a rebellious night in the school’s sealed-off basement, Vicki and her friends inadvertently unseal Mary Lou’s long-forgotten trophy trunk. This act of teenage curiosity shatters the barrier between the living and the dead, releasing Mary Lou’s vengeful, demonic spirit into the halls of Hamilton High.Driven by an insatiable thirst for
unfinished business and bloody vengeance, Mary Lou possesses Vicki's body. Her primary motivation is twofold: she wants to complete the prom night that was stolen from her and exact a brutal revenge upon Bill Nordham, who ruined her life three decades prior. As Mary Lou exerts control over Vicki, the quiet, conservative teenager undergoes a drastic, alluring transformation into a hyper-sexualized, 1950s siren.The school soon becomes a chamber of horrors as Mary Lou embarks on a sadistic killing spree. She targets anyone who stands in her way or crosses her path, utilizing supernatural powers to orchestrate gruesome demises. A teacher is burned alive inside a tanning bed, a rebellious student is impaled by flying gym equipment, and another is brutally murdered with a curling iron. Throughout this terrifying escalation, Principal Bill realizes with mounting dread that his past sins have returned to claim him.Vicki’s pious mother, Rita, who was also present on the fateful night in 1957 and helped cover up Bill's culpability, senses the demonic presence. Rita attempts to use her religious faith to banish the evil entity, enlisting the help of a local priest to perform an exorcism. However, Mary Lou is too powerful, effortlessly dispatching the priest and turning her sights toward the climax of her grand design: the 1987 senior prom.At the dance, Mary Lou—fully in control of Vicki—manipulates the election so she is once again crowned prom queen. As she prepares to claim Principal Bill as her final sacrifice, Craig and Rita intervene, sparking a frantic supernatural showdown. Utilizing a combination of maternal sacrifice and holy relics, they manage to trap the spirit and cast it back into the spiritual realm, saving Vicki's life just as the cursed prom night comes to a fiery, chaotic end.