In the opening scene, we meet four high school girls who possess both beauty and charisma, aptly dubbed the "Flawless Four." These girls reign as the most popular at Reagan High School in Southern California. The group comprises Courtney Shayne (Rose McGowan), known as the "Satan-in-heels"; Marcie Fox (Julie Benz), affectionately called 'Foxy'; Julie Freeman (Rebecca Gayheart); and Elizabeth Purr (played by Charlotte Ayanna), renowned as the "Princess Di of Reagan High." Among them, only Elizabeth is genuinely kind-hearted, cherished by all. Unfortunately, Julie's popularity seems guaranteed thanks to her striking appearance and her tight-knit friendship with Elizabeth. Meanwhile, the cold-hearted queen bee Courtney and her ditzy companion Marcie instill fear to command respect.
On the morning of Elizabeth's seventeenth birthday, the trio—Courtney, Marcie, and Julie—play a cruel prank: they fake kidnapping her. Their plan involves gagging her with a jawbreaker candyball and binding her with ropes before stuffing her into the trunk of a car. As they drive off, their intention is to take the helpless girl out for pancakes. However, upon opening the trunk later, they are met with a horrifying scene: Liz has tragically choked to death, the jawbreaker having obstructed her airway.
In a state of shock and horror, Julie suggests going to the police, but the manipulative Courtney forbids it. Instead, she impersonates Liz's mother and informs the school that Liz is too ill to attend. Continuously trying to cover their tracks, Courtney, Marcie, and Julie return to school, acting as if nothing has happened. It isn't long before school outcast Fern Mayo (portrayed by Judy Greer) is sent by the principal to deliver Liz’s homework. In a shocking twist, she discovers the girls’ dark secret when she stumbles upon Liz's disfigured body. Consumed by envy, Courtney concocts a narrative, claiming Liz fell victim to a rapist, aiming to tarnish her angelic reputation and portray her as a rebellious girl instead.
Fern, who idolized Liz, is horrified but quickly captured by the notorious girls. To keep Fern quiet, Courtney offers her a spot in their clique, proclaiming that she will replace Liz. Under Courtney and Marcie’s influence, Fern undergoes a dramatic transformation, shifting from the awkward outcast to the stunning new girl Vylette. As the new façade emerges, Julie grapples with immense guilt, distancing herself from her peers, only to face bullying from her former friends and becoming a target of their cruelty. The only comfort she finds is in her relationship with her drama-loving boyfriend, Zack.
Meanwhile, Detective Vera Cruz (played by Pam Grier) begins to unravel the mystery behind Liz's untimely death after her parents return from a trip. The principal, Ms. Sherwood (Carol Kane), cooperates to assist in the investigation, but Courtney, Marcie, and Julie maintain a united front, denying any involvement. Fern/Vylette’s peculiar manner raises eyebrows, yet without substantial evidence, Cruz reluctantly allows her to remain at large.
As Vylette's popularity skyrockets, Julie watches in dismay as Courtney weaves a tangled web of lies to evade responsibility for Liz's murder and hold onto her social standing. To her disgust, Julie learns from Detective Cruz that Courtney had the audacity to engage in sexual acts with a stranger in Liz's bed, fabricating an even worse cover-up to suggest Liz had been raped.
Driven by an overwhelming sense of competition, Vylette revels in her fame, overshadowing even Courtney. Aware she has unleashed a monster, Courtney threatens to blow Vylette's cover, only for Vylette to counter by promising to reveal the truth about Liz's demise if threatened. Tempers flare when Courtney and Marcie distribute enlarged yearbook photos of Fern with the question "Who is Vylette?" plastered across them, humiliating Fern in front of the entire student body.
Feeling a sense of pity for Fern, Julie reconciles with her and sifts through Liz’s belongings that she was given posthumously. During her search, she finds the recording card that inadvertently captured Courtney's confession, "I killed Liz! I killed the teen dream! Deal with it!" This discovery ignites a daring plan that involves Julie, Fern, and Zack rushing to the senior prom to unveil the truth.
As Courtney and her jock boyfriend Dane Sanders (Ethan Erickson) are crowned Prom King and Queen, Zack stealthily broadcasts the incriminating confession over the sound system during Courtney’s acceptance speech. As shockwaves ripple through the crowd, Dane quickly recoils from Courtney in horror, prompting Marcie to flee in embarrassment. Facing the fallout of her actions, Courtney attempts to escape the chaos, only to be met with the furious student body hurling corsages at her while labeling her a murderer. At the culmination of the event, Julie stands ready at the exit, capturing the moment with a photo of Courtney's anguished expression, ensuring that the nightmare of her reign is forever immortalized.
