A boy falls to his death at school, but Ok Chan-mi does not believe that her twin brother, Park Won-seok, committed suicide. Chan-mi transfers to her brother's school, Yongtan High, and meets Ji Soo-heon, who witnessed her brother's death. A "hero," who avenges bullied students, appears at Yongtan High. Chan-mi speculates that it may be connected to her brother and starts looking for this hero.
Chanmi transfers to her twin brother's school to find out the truth about his suicide.
Chanmi learns a shocking truth of a different life that her brother lived.
Sooheon punishes Sa Jungkyung and is called a hero by the students, but Chanmi grows suspicious.
There is a scheme to kick Chanmi out of school, and Sooheon advises her to leave.
Wonseok's case is reclassified as a homicide. Chanmi learns of Wonseok's lie to her.
Sooheon finds himself in a predicament as he becomes number one suspect of a murder.
Chanmi gets an unbelievable call, as she holds Sooheon at gunpoint.
Chanmi and Sooheon are convinced that Gi Osung is Wonseok's killer.
Sooheon revisits Sa Jungkyung's camping car, but it is a trap.
Osung feels betrayed as his plan fails. Chanmi makes a shocking discovery as she sets up a trap.
Jaebum regains his memories, but Sooheon is unfamiliar with this version of Jaebum.
As truths emerge, the time for the final revenge has come.
