Megan Paige (Eliza Dushku) is an investigator for the Rochester Police Department who is assigned to investigate the murder of a young girl named Carla Castillo, whose body is found in the nearby village of Churchville covered in cat hair. Against opposition of her colleagues and partner-boyfriend Kenneth Shine (Cary Elwes), Megan insists that the murder is a work of a serial killer. Despite Megan’s considerable efforts, she fails to catch the killer. Stress and obsession of the investigation causes Megan to hallucinate the victim's image. She ultimately has a nervous breakdown and tries to commit suicide.
Following two years of medical treatment and attending mental illness support group headed by Richard Ledge (Timothy Hutton), Megan rejoins the police department in a clerical Job. However following a similar murder of another young girl Wendy Walsh whose body is found in Webster covered in cat hair, Megan insists on reentering the investigation. Partnering with Steven Harper (Tom Malloy), they try to find common threads between two girls. But no sooner does she start the investigation, another girl named Melissa Maestro is killed. They find a number of commonalities between Wendy and Melissa, but fail to connect these to the first victim. Meanwhile, Webster police department who is also working on the case, receives a call from 19 year old Elizabeth Eckers that she is being kidnapped in a house. Convinced that the suspect is not the Alphabet killer, Megan tries to stop the police raid but fails to do so. The police declare that they have killed the Alphabet killer and provide evidences present in the house including same cat hair as seen on three victims.
Certain that the Webster police planted the evidence in order to justify killing the innocent, Megan continues the investigation on her own. On revisiting her first case, Megan finally finds that all three girls attended the St. Michaels Church in Rochester. Still suffering hallucination of victims, Megan visits the church and tries the question the pastor but suffers another breakdown and is hospitalized. Megan flees from the hospital and takes refuge in Richard's home. There she finds that Richard used to work for the St. Michaels Church and is in fact the killer, but before she could act Richard knocks her unconscious and drives off to a remote place to kill her. Megan however eludes him and ultimately shoots him. Richard falls into a stream of water nearby. Unsure whether Richard is dead and confused by her surroundings, she suffers another breakdown.
Finally, Megan is hospitalized and kept under intensive psychiatric care. Richard survives the attack and is seen in a church at unknown location.