Asian Drama

The story of the investigative team Number 5 specially organized to actively combat crime through stake outs, wiretapping, communications monitoring, and deep-cover infiltration. A secret police unit that bends the limits of the law in order to fight crime, the new department comes in addition to the existing departments for criminal investigations, special investigations, criminal affairs, and white collar crime.

The members are Cha Gun-Woo, Jang Moo-Won, Jang Min-Joo and Choi Tae-Pyeong. They will hunt down criminals and investigate crimes while undercover (hence the title).

A pawnbroker is found murdered in a remote town. Police suspect that he was murdered by an acquaintance, as even the most experienced investigator on the case could identify no signs of resistance. Three people come under suspicion but all of them have perfect alibis and the investigation comes to a standstill. One year later, one of them is found dead and the original murder case becomes even more mysterious. Almost fifteen years pass and the lead inspector, now approaching retirement, reflects on the only case he could not solve in an otherwise successful career. Haunted by a sense of responsibility and guilt that he caused suffering by letting the murder case go unsolved, he decides to re-investigate. His persistent search brings attention to the long forgotten case and reveals a hidden relationship between the victim's son and the neighborhood woman's daughter. As their love grows, more crimes happen. As their sin grows, the inspector's chase comes closer to them.

Jang Geu Rae has played the game of Go since he was a child. When his plans of becoming a professional Go player fail, the down-and-out Geu Rae is forced to take an office job as an intern set up for him by an acquaintance’s recommendation for him to a large company called One International.

On his first day of work, Geu Rae meets an eager fellow intern An Yeong Yi as they both try to please their new boss, Section Chief Oh Sang Shik, and keep up with the ambitious employee Jang Baek Ki. But they quickly find that their department is a little different from the others.

Geu Rae does his best at his new job while trying not to lose his humanity along the way.

20 years ago Moo-Yeom’s (Yoon Sang-Hyun) father was a suspect in the "Gap Dong” serial murder case. Because of the detectives’ oppressive investigation, Moo-Yeom’s father killed himself. Now, Moo-Yeom is a detective and works to capture the killer Gap Dong. The statue of limitations has expired for the serial murder case and Moo-Yeom resigns to the belief that Gap Dong is dead. New clues though for Gap Dong appears in front of Moo-Yeom and he sets out to catch him once and for all.

Inspired by the "Hwaseong serial murder case".