Four police officers are recruited as part of a secret police unit that was formed to battle violent crimes. Jang Moo-Hyun is a veteran police officer who decides to form a secret team dubbed “Investigative Team 5”. He forms the squad under the conditions that he would be solely responsible for everything that happens to the team. He recruits three other adept officers to be part of his unit. The new recruits all have past wounds and secrets that will be unraveled throughout the show.