The film tells the story of a contract martial arts officer under the Ministry of Justice who closely manages parolee subject to electronic ankle bracelets, assists probation officers in their work, and suppresses verbal and physical abuse and violence that occurs in emergencies with martial arts.

Lee Jung-do is a black belt in taekwondo, kendo, and judo who spends his days playing video games with his nerdy friends when not working as a delivery rider for his father's fried chicken restaurant.

Notorious child molester Kang Ki-jung is released from prison on parole and Sun-min and Jung-do are assigned to keep tabs on him.

A young girl is kidnapped by them and Sun-min, Min-jo and Jung-do are tricked into going to different locations as a distraction where they are ambushed by former parolees seeking revenge.

Min-jo is killed and Sun-min is left with a serious neck injury in the ambush but Jung-do manages to escape his attackers.