A boy falls to his death at school, but Ok Chanmi does not believe that her twin brother, Park Wonseok, committed suicide. Chanmi transfers to her brother's school, Yongtan High, and meets Ji Sooheon, who witnessed her brother's death. A "hero," who avenges bullied students, appears at Yongtan High. Chanmi speculates that it may be connected to her brother and starts looking for this hero.
