By day, Kim Ji-yong is a model student at the National Police University; by night, he punishes criminals who have escaped legal justice as the vigilante. Traumatized by seeing his mother’s killer receive a light sentence, he decides to take justice into his own hands. As Vigilante’s actions draw public attention, Jo Heon of the Metropolitan Investigation Unit pursues him, while DK Group’s vice chairman, Jo Kang-wook, tries to use him for his own ends, and reporter Choi Mi-ryeo seeks headlines. Ji-yong investigates the crimes of Kim Sam-doo, head of a major crime organization, and corrupt police official Eom Jae-hyup; after a colleague’s sacrifice and realizing legal justice will not prevail, he personally punishes both men. Afterwards, the media obscures the truth about Vigilante’s identity and Eom’s fate. At his police graduation, Ji-yong silently walks away, suggesting his battle is far from over.