Detective Jin Kang-ho investigates the murder of a school teacher but is unable to find any meaningful evidence. Meanwhile, Kang Mu-young, a television producer of a reality crime show, tries to crack an unsolved case on her own.

After being forced to release the suspect due to lack of evidence, Kang-ho gets suspended for going after the heir of a conglomerate. Unwilling to stand down, Kang-ho teams up with Mu-young without the department's approval.

Jang Min-gi, a serial killer, successfully escapes imprisonment, leading to further murders. Kang-ho realizes that Jang Min-gi is not acting alone and discovers a link between him and a private investigator named Tak-won.

Kang-ho realizes that Jang Min-gi is not the serial killer, but the higher-ups decide to exclude him from the investigation. Kang-ho teams up with Mu-young yet again, and they discover the link between Teddy Jung and Tak-won.

Tak-won is shot, and Teddy Jung is gravely wounded. The police identifies Jang Min-gi as the serial killer, but Kang-ho carries on with the investigation independently. Meanwhile, Mu-young looks into a mob boss named Lee Tae-sung.

The body of a middle school student is discovered after 10 years, and Detective Min Daejin is surprised to discover that he went to school with the victim. Meanwhile, Lee Ban-seok's daughter goes missing, and Mu-young receives a dangerous tip-off.