The film starts with a 12-year-old girl whose babysitter is on a date with serial killer Patrick Bateman. After Bateman kills and starts to dissect her babysitter, said 12-year-old girl stabs him with an ice pick. Fast forward to the present day and the girl, who is named Rachael Newman, is now a college student studying criminology under Professor Starkman, a former FBI agent. Rachael aspires to join the FBI and is determined to get the teaching assistant position under Starkman, which would make her a shoo-in for the FBI training program.

Tough competition for the position stands in her way, and Rachael proceeds to kill off classmates one by one. During her killing spree, she decides to see the school psychiatrist, Dr. Eric Daniels. Realizing that Rachael is a textbook sociopath that is obsessed with Starkman, Daniels tries to warn Starkman but without revealing Rachel's name due to patient confidentiality. Starkman mistakenly assumes that the student obsessed with him is Cassandra Blaire, with whom he had an extramarital affair. When Cassandra reveals that her affair with Professor Starkman has guaranteed her the TA position, Rachael decides to murder her as well. After she does so, Professor Starkman discovers Cassandra's body and calls Daniels to tell him that "she's dead". However, he does not identify the victim and Daniels assumes it must be Rachael. Distraught, Professor Starkman leaves his teaching position, which angers the obsessed Rachael. It is revealed that she is not Rachael Newman; she killed the real Rachael at the beginning of the semester and assumed her identity.

During spring break, "Rachael" stays on campus and locates an intoxicated Starkman, impaired by the effects of Valium and alcohol, and tries to seduce him to get the job. However, Starkman sees she is wearing a dress and necklace he had given to Cassandra. She then confesses her crimes to him, her "crush" on him, and that she knew about his affairs with various women (which included her former babysitter that Bateman murdered), as he backs up towards the window in a state of confusion and fear. Rachael blows him a kiss, and he falls out the window to his death. As she leaves, Rachael also murders a janitor and a security guard because they witnessed Starkman's death.

As the film reaches its conclusion, Daniels and two cops pursue Rachael in a car chase, which ends with Rachael driving off a cliff, resulting in the car exploding. At this point, she is presumed to be dead by the cops who witnessed the event and the media.

Two years later, Dr. Daniels is giving a lecture on Rachael's mind and how he wrote a book about her. When he looks up from speaking with a student, he sees Rachael, who has not died after all; she indirectly reveals that she killed Starkman's last assistant, Elizabeth McGuire, and stole her identity to get into Quantico FBI Academy. She allows Dr. Daniels to know because she believes there is no point in committing the perfect crime if no one knows about it and she is confident he will not divulge this information because it would make a farce of his best-selling book in which he claimed to completely understand her and witness her death in the fiery car. The body that was in the car was the real Rachael, whose decaying body had been kept in the killer's dorm closet. It was revealed by another student that Rachael is the youngest agent to be drafted to the Bureau in her sophomore year. As Rachael walks out of his class, Dr. Daniels is visib