An undercover detective is murdered, and the chief of police summons Oh Gu-tak to investigate.

Tasked with catching the Northeast Serial Killer, the Bad Guys each begin their own investigations.

The Bad Guys launch a full-scale investigation to find a victim of organ trafficking.

The Bad Guys uncover the shocking truth behind an underground human trafficking organization.

The Bad Guys are tasked with catching a serial shooter who has killed 12 people.

Woong-chul is kidnapped and almost buried alive by Doo-gwang. The Bad Guys go to investigate.