Recently divorced, Yoo-lim (Yoo Sun) now lives with her only daughter, Eun-ah (Nam Bo-ra). Upon arriving at her new school, Eun-ah is frequently picked on, though she has feelings for classmate Jo-han (Shin Dongho). One day she is brutally raped by Jo-han and his friends who threaten to upload footage of the rape online to keep her quiet. Unable to cope with the trauma she was forced to endure, Eun-ah takes her own life. As all of the boys involved in the rape are still minors, the law is helpless to prosecute them to the fullest extent possible, and they walk away with little more than a slap on the wrist. Filled with frustration and anger, You-lim sets out to make the boys' lives a living hell. As You-lim's animosity and exasperation is transformed into ever more brutal acts of revenge, she is brought closer and closer to the edge of insanity.