Violet Rue Kerrigan is a ninth-grade girl who lives with her Aunt Irma and Uncle Oscar, since her own father has abandoned her. A quiet girl, she is often bullied by the boys at school. The story centers around a seven-month-long sexual abuse of Violet by her math teacher, Mr. Sandman, and is told in ten mini chapters. The story is told in the first person, but not linearly, jumping back and forth in time and interwoven with parentheticals and italicized inner thoughts.

Mr. Sandman is a middle-aged math teacher known for his traditional, often severe, teaching methods. He favors the rich, white male students and gives the other male students demeaning nicknames. He firmly believes that his female students don't have a "natural aptitude" for math, so expects only mediocrity from them. He does hold private "tutorials" for the girls, giving them extra help and revealing test questions ahead of time. During these tutorials, he takes a liking to Violet, noticing she is an unusually promising student, for a girl.

One day, Violet is chased by some bullies around the parking lot. Desperate, she finds an open car door, hops inside, and hides under a coat. The boys leave her. Then, Mr. Sandman opens the door and she realizes it's his car. He expresses sympathy, calls her "Sleeping Beauty" and agrees to drive her home. He does not drive her home, though, and instead takes her to his house, where he makes her a hot chocolate laced with a sleeping drug. Violet wakes up hours later, dazed and with her shirt buttoned crookedly. Mr. Sandman drives her home, telling her their "tutorial" will be their little secret, and to tell her aunt she has been selected as secretary of a competitive Math Club and must attend afterschool meetings.

Violet's "tutorials" with Mr. Sandman become more frequent, though it is not clear how often the abuse occurs. The routine is always the same: Mr. Sandman will make her a hot drink laced with a sleeping drug, then prattle on about Hitler and eugenics (he is a raging neo-Nazi and white supremacist) until she falls asleep. She'll wake later, sometimes in a state of undress, sometimes even naked in a silk robe, freshly bathed and covered in lotion. Mr. Sandman asks to measure her once, and uses a tape measure to record her measurements and her weight. One time, Violet wanders into a room and finds two decades worth of neatly catalogued photo albums, all filled with photographs of white, prepubescent girls, fast asleep and in sexual positions, each accompanied by measurements and even clippings of hair. Violet notices one photograph in which a girl is awake and reaching toward the camera with a fearful expression.

One night, Mr. Sandman gives Violet too much of the drug and she won't wake up. Panicked, he drives her to the ER, where he drops her in the waiting room and tries to drive away. But in his distress, he crashes his car into a van and is then arrested. He later pleads guilty, and is found to have been a serial abuser for decades.

But after Mr. Sandman is arrested, Violet is not compliant with authorities and therapists, and refuses to condemn her abuser. She does not want to remember the traumatic events, and claims she cannot remember. She even has positive thoughts about Mr. Sandman, remembering him as a savior from high school bullies, and remembering his actions towards her as tender and loving. The text is interwoven with italicized questions, implied to be from therapists or officers, asking her why she kept going back to his house, why she didn't run away — implicitly placing blame on her. In the final scene, she lies in bed under a blanket and tries to remember Mr. Sandman's face.