Mouse

A serial killer named Headhunter is terrorizing the country but is hiding in plain sight. Daniel Lee has identified a gene that can predict whether the baby is a psychopath 99 percent of the time.

Decades into the future we see what became of the Go brothers and the headhunter. Bo Reum is at the prison entertaining prisoners with a magic show when he gets a devastating surprise.

Ba Reum realizes that Chi Kook's watch was found on a new victim and notifies Moo Chi. Bong Yi's grandmother sees something she shouldn't and is terrified by her finding.

Moo Chi feels that something is suspicious about Sung Yo Han, but he can't find any evidence yet. A boy 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.

An hour-long live broadcast goes on air in hopes of saving Han Kook. During the live broadcast, endless tip-offs and reports from former victims of the predator flood into the broadcast station.

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, he starts investigating Bong Yi's grandmother's case.

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.

Ba Reum's instinctive intuition helps Moo Chi get closer to the bottom of the mystery behind the knots. While investigating the suspects, Moo Chi and Ba Reum spot a man who stands out from the rest.

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.

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. Reum is terrified that the Yo Han inside him might take him over completely.

Ba Reum keeps hearing Yo Han's voice in his head telling him to kill people. 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 keeps a close eye on Kang Duk Soo's murder investigation. 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.

The DNA result found on the weapon that was used to kill Kang Duk Soo confuses Moo Chi. Bong Yi joins Hong Ju's team and starts investigating the Suseong serial murder case.