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 keeps hearing Yo Han’s voice in his head telling him to kill people. The hallucination eventually made him murder Woo Hyung Chul. When he goes to the station to turn himself in, he finds out all the evidence related to his murder is gone, including Woo Hyung Chul’s body. Bong Yi runs into Kang Duk Soo, which makes her anxious. On a rainy day, Kang Duk Soo starts making a move again.

Ba Reum finds himself acting a lot more violent than before and realizes that it’s getting harder to control himself. He even gets the urge to kill someone. While Ba Reum is terrified that the Yo Han inside him might take him over completely, another murder case occurs that shows the MO of the previous murder cases. If Yo Han wasn’t the culprit of the serial murders, then is the piece of brain transplanted into Ba Reum’s head not of a psychopath?

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.

Ba Reum’s instinctive intuition helps Moo Chi get closer to the bottom of the mystery behind the knots. But he suffers from the random flashbacks that seem very unfamiliar. While investigating the suspects, Moo Chi and Ba Reum spot a man who stands out from the rest. On the other hand, Kang Duk Soo, who has been released from prison keeps trying to find out where Bong Yi lives.

After getting a gunshot wound, Yo Han is in critical condition. Ba Reum gets brain surgery. But after receiving the brain surgery, he suffers from memory loss. After a year, Moo Chi is assigned to a new team that collects and organizes criminal evidence. Ba Reum starts to work for a small precinct. On his first day at work, he accidentally finds a dead body.

After Moo Won is brutally murdered, Moo Chi gives up on everything and only keeps drinking. While Han Kook is still missing and his life is under threat, the police haven’t found any clues on the culprit. When Moo Chi gets back on his feet and starts investigating Bong Yi’s grandmother’s case, he finds out about Yo Han and his mother.

An hour-long live broadcast goes on air in hopes to save Han Kook. But Ba Reum sets off to a discreet journey as the rest struggle hard to find out the predator’s motive of murder. During the live broadcast, endless tip-offs and reports from former victims of the predator flood into the broadcast station. The investigation seems to progress in a positive outlook as Moo Chi narrows down the suspects. Will they be able find the murderer in time?

After Bong Yi’s grandmother is murdered and a mysterious finger is found at a church, Moo Chi and his team start investigating more thoroughly. Moo Chi feels that something is suspicious about Doctor Sung Yo Han, but he can’t find any evidence yet. A boy suddenly gets kidnapped and Moo Chi gets a call from the kidnapper. He demands Moo Chi to find out the reason why the boy had to be kidnapped before a certain time. Will Moo Chi be able to save the kid?

Chi Kook has been found at the prison with multiple stab marks all over his body along with a message written in blood. Not long after that, Chi Kook’s watch, a present gifted by Ba Reum and Dong Koo, was retrieved at the grape farm murder site, leading Ba Reum to join Moo Chi for the investigation. Meanwhile, Bong Yi’s grandmother stumbles upon something she should’ve never found out while working as a cleaning lady for Bong Yi’s settlement money.

Moo Chi visits the Head Hunter at the prison and tells him that he’ll not only kill the Head Hunter but find his son and make him suffer as he did. Meanwhile, more murder victims are found in a row and the culprit is leaving leads, asking to be noticed. When Ba Reum visits Moojin Prison, he sees the Head Hunter and also witnesses another murder case.

Terrifying news of an unsolved serial killing case strikes the country, putting everyone in fear. One day, a family of four visits a camp site just to face a horrible death by this very serial killer, Head Hunter. A boy survives the ambush and later on pinpoints the prime suspect as the killer. Meanwhile, a gene test to verify an unborn fetus for its potential psychopathic characteristics is carried out on Head Hunter’s baby, and the baby’s mother has to make a choice.