The film opens with Donna (Brittany Snow) returning home from a movie outing with her friend Lisa and Lisa's mother. After their farewells, Donna and Lisa briefly chat about cheerleading tryouts, but Donna is hesitant to participate this year, as it's her sophomore year. Upon arriving home, Donna hangs up her jacket but finds her house eerily quiet, with the television running in the background. As she calls out to her family, a chilling silence greets her.
When Donna hangs her jacket in the closet, she thinks she hears a sound behind her but finds nothing there. Moving past the couch, the camera reveals the horrifying truth: her father's lifeless body lies at the bottom, a gruesome cut across his throat. Distraught, she heads upstairs and unintentionally trips over her brother's baseball bat, which lets out a small shout. Rushing into her brother's room, she finds him sprawled on the bed, only to discover the chilling evidence of his demise when she pokes him lightly, revealing the wound on his throat.
Panicking, she hears a man yelling, "Where is she?" and instinctively hides under the bed. Through her hiding place, she witnesses her mother's brutal encounter with Mr. Fenton (Scheach), who, demanding to know Donna's whereabouts, violently attacks her mother. Covers in terror, Donna watches as the horrific scene unfolds: her mother is brutally stabbed multiple times. When the chaos finally subsides, Donna escapes downstairs to signal passing police. Just as she thinks she has made it to safety, she hears the killer's voice whispering, "I did it for us," sending her screaming into darkness.
Fast forward, and we find Donna in a school psychiatrist's office recounting her harrowing nightmares about that fateful night. "What happens next?" the psychiatrist queries, to which Donna responds, "And then I wake up, just like I used to." The doctor reassures her that the killer is incarcerated and can only invade her dreams. The conversation shifts, leading Donna to reminisce about her upcoming prom dress with her friends Lisa and Claire (Stroup) while getting ready at a beauty salon.
As they prepare for the big night, Donna catches a glimpse of the killer in the reflection of her mirror, sending chills down her spine. Later that night, getting ready for prom, she and her longtime boyfriend Bobby (Porter) share an emotional exchange while taking pictures and exchanging corsages.
Meanwhile, at the police department, Detectives Winn (Elba) and Nash (Rinsone) uncover the disturbing truth: the killer has escaped from prison, and an obsession connected to Donna's life is at the center of the chaos. Probing deeper into Donna's past trauma reveals the chilling involvement of a former teacher who unleashed a string of violence against her family.
At prom in a lavish hotel, tensions rise as friends spot an adversarial classmate named Crissy (Davis). When one of Donna's friends, Ronnie, fetches room keys for their stay that night, the killer, posing as someone else, begins to stalk the group with malicious intent.
As the prom unfolds, a series of terrifying events occur: a housekeeper is brutally slaughtered, and the killer soon makes his presence known to Donna's group. The night spirals into a frenzy of terror, with Claire and her date Michael (Blatz) falling victim to the rampage. As chaos ensues, the remaining friends search desperately for each other, unaware of the lurking danger.
Donna finds herself isolated and terrified, confronting her demons as the killer advances closer. In a series of intense sequences, she narrowly escapes his grasp time and again. As the situation escalates, Detective Winn realizes the killer may have already infiltrated their vicinity, leading to a frantic police response.
In a heart-stopping climax, the truth begins to unravel when Donna faces the horror of realizing the shocking nature of her reality. Finally, with sheer determination, she battles against her fear and fights for survival in an intense encounter. Detective Winn intervenes at the last moment, delivering a powerful closure to the terror that has plagued Donna for so long. "It's over," he assures her, marking the end of her nightmare.
