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.
Episode 1
Chan-mi transfers to her twin brother's school to find out the truth about his suicide.
Episode 2
Chan-mi learns a shocking truth of a different life that her brother lived.
Episode 3
Soo-heon punishes Sa Jung-kyung and is called a hero by the students, but Chan-mi grows suspicious.
Episode 4
There is a scheme to kick Chan-mi out of school, and Soo-heon advises her to leave.
Episode 5
Won-seok's case is reclassified as a homicide. Chan-mi learns of Won-seok's lie to her.
Episode 6
Soo-heon finds himself in a predicament as he becomes number one suspect of a murder.
Episode 7
Chan-mi gets an unbelievable call, as she holds Soo-heon at gunpoint.
Episode 8
Chan-mi and Soo-heon are convinced that Gi O-sung is Won-seok's killer.
Episode 9
Soo-heon revisits Sa Jung-kyung's camping car, but it is a trap.
Episode 10
O-sung feels betrayed as his plan fails. Chan-mi makes a shocking discovery as she sets up a trap.
Episode 11
Jae-bum regains his memories, but Soo-heon is unfamiliar with this version of Jae-bum.
Episode 12
As truths emerge, the time for the final revenge has come.
