Kim Geonwoo, a student at the prestigious Haneum International Middle School, is discovered unconscious by the lake with a letter that contains the names of four of his classmates: Do Yoonjae, the son of the Chairman of the Hospital Board, Park Kyubeom, the grandson of the former Chief of Police, Jeong Ideun, the son of a teacher at Haneum International Middle School, and Kang Hangyeol, the son of Attorney Kang Hochang. The perpetrators' parents try to cover up the incident using their authority and financial power. But, when homeroom teacher Song Jeonguk's confesses, Geonwoo's mother learns the truth about her son's death, and Haneum International Middle School is put under the spotlight. revealing the true colors of the parents of the perpetrators. When a child becomes a monster, their parents become the devil.