Ba Reum makes the final decision to turn himself in and finish one last mission that only he can do. Hong Ju also shares her big secret that’s been tormenting her for years on her last show with Hee Jin, a woman who in fact was a secret agent working for Choi Young Shin under a massive private organization.
Moo Chi and Bong Yi get closer to the truth. In the meantime, Ba Reum tries to find his aunt, the last missing puzzle piece. Sang, who tries to confirm Ba Reum’s alibi, finds something suspicious at Ba Reum’s house.
Moo Chi finds out that Ba Reum was the killer and ferociously charges after him at the station. Moo Chi also suspects Detective Lee being part of the OZ organization and tries to carry out an investigation on the two, but it’s not easy. As flustered as he is, Ba Reum tries to remain calm to buy time until he figures out the killer of Chi Kook.
Ba Reum finally remembers what exactly happened to his family. He tries to set a trap to catch the mysterious OZ, and he finds out a secret about Dr. Daniel Lee in the process. Meanwhile, Moo Chi finds the unregistered car the OZ, the murderer who killed Chi Kook, used.
Chi Kook’s sudden death shocks everyone and Ba Reum tries to convince Chi Kook’s mom in requesting an autopsy. Meanwhile, Detective Ko starts to doubt that Sung Yo Han was the real killer. He starts to dig deeper into Song Soo Ho’s past.
After killing Kang Duk Soo, Ba Reum keeps a close eye on how the investigation rolls out. He tries to keep a foot ahead so his murder stays unveiled. Bong Yi on the other hand, thinks Moo Chi was the killer of Kang and keeps her mouth shut even when she’s being speculated as a suspect.
Ba Reum finds out about a shocking story behind his brain surgery a year ago. He’s tormented by unwanted memories that keep haunting him. Detective Ko is furious at Han Seo Joon’s remark of being saved and being at peace after accepting Christ and decides to kill him himself.
A psychopath's ruthless serial murders have left the entire nation gripped with fear and chaos. A honest and justice-seeking rookie police officer and a veteran detective with tragic past, face against the killer. After the encounter with the psychopath, their lives totally change.