The main characters of the book are Ashley Patterson, an introverted workaholic, her co-workers, Toni Prescott, an outgoing singer and dancer, and shy artist Alette Peters and Ashley's father.

The three women do not get along very well, because of their dissimilar natures. Toni and Alette generally maintain a friendship, with Alette a calming influence, but Toni dislikes Ashley and criticizes her harshly. All three have issues with their mothers having told them they'd never amount to anything.

Ashley fears that somebody is following her. She finds her house lights turned on when she returns from work, her personal effects in disarray, and someone has written "You will die" on her mirror with a lipstick. She thinks someone's broken into her house. She requests a police escort, but the next morning, the police officer assigned to this duty is found dead in her apartment. Two other murders have already taken place, with an identical pattern. All the murdered men had been castrated and were having sex before being murdered. Evidence points to the same woman being involved in all three cases. When a gift from one of the murdered men to Toni is found among Ashley's things, she is identified as the killer and arrested. At this point, it is revealed that the three women are three selves of a woman suffering from multiple personality disorder.

Ashley's father persuades an attorney friend to represent Ashley. The second half of the novel deals with the trial, complete with endless squabbling between opposing psychiatrists as to whether or not MPD is real. Finally when Ashley's advocate introduces Toni, the violent alter of Ashley, the court is convinced that Ashley is innocent. Ashley is committed to an insane asylum and in the course of therapy is introduced to her two "alters" and relives the horrific events that shattered her mind. She was sexually abused during her childhood, and this made her to develop a strong hatred towards men.

In the asylum, Ashley is treated for MPD by doctor Gilbert. He is attracted to her and during her crisis, he too feels her pain and wants to comfort her. In the end, Doctor Gilbert releases her from the asylum as he believes she is cured. It is revealed that her father was the one who sexually abused her, and caused her to develop Dissociative Identity Disorder.