Yu graduated from the Faculty of Literature at a national university and once aspired to be a literature researcher. She married her husband whom she met while she was still a student, and now has a son who attends high school. They lived a busy but peaceful life, but one day, her son brought his friends over and decided to hold a study group. As she spent time with her son's young and strong friends, Yu's hidden sadistic personality began to emerge. So Yu decided to teach him not only school studies but also sexual matters...