A detective who was chasing the real culprit of a serial murder case faces the hidden secret of his family. Jin-sung is a cheerful yet nasty-tempered detective at Woojin Police Station who fights for justice with all his heart. Meanwhile, Young Ju is a competent prosecutor with a high winning rate who believes that injustice must be punished through injustice. She is also an old friend of Jin-sung and Jin-woo. Jin-sung transfers to a special investigation team in Seoul for serial murder cases and carries out the investigation with Young-ju. However, Jin-woo, Jin-sung's brother, gets arrested as a suspect of the serial murders.

Jin-woo gets released and Jin-sung manages to obtain crucial evidence to arrest Bae Min-gyu. However, when the arrest warrant was issued, another suspect of the three serial murders appeared. Meanwhile, Jung-sook wants Young-woon to quit his job and move to the US with the family.

On a stormy night, Jin-woo gets into an accident at the seaside. Jin-sung and Young-ju get help from Jung-sook to transfer him to Jinjin Medical Center in Seoul. He may be brain-dead in the worst-case scenario, but Jin-sung and Young-ju believe that he will wake up. Meanwhile, Young-woon is being sent to training abroad as a reward for solving the serial murder.

Jin Sung receives two videos sent by an anonymous sender, and he’s shocked to discover that the videos show his brother Jin Woo being murdered. Similarly, Ko Young Ju also receives a video of a murder with a warning that the real culprit is someone else. These revelations lead the special task force to reopen the case, and they uncover new leads in their investigation.

The Special Task Force was able to identify the source of the leak about the warrant, but the damage had already been done. The team is to disband, and prosecutors Young Ju and Young Woon face disciplinary action. However, this isn’t enough to stop the team, as they identify a new suspect.

Jin Sung is shocked at discovering Park Ki Young’s room is identical to Young Woon’s room. He alerts Hee Ju, who is still with Ki Young, of his findings. However, it is too late as Hee Ju is kidnapped by Ki Young. With the police searching everywhere for Ki Young, the Task Force set up a trap anticipating that he will try to get in contact with Min Gyu.

Jin Sung arrives at Young Ju's apartment only to find out that he is late and she has already been kidnapped. Now, Jin Sung must locate Ki Young before he harms Hee Ju and Young Ju. Even though the police are looking for Ki Young, he remains confident of his perfect crime. Will Jin Sung and Young Woon be able to successfully arrest Ki Young and rescue Hee Ju and Young Ju?

Park Ki Young is found dead, and now Ko Young Ju and Cha Young Woon must charge Bae Min Gyu with the serial murders. The chief prosecutor is relieved to see his daughter back safely and wants to close the case, but Young Woon and Young Ju sense there's more to Ki Young's death and request further investigation.

Jung Woo No instructed Dr. Chu to monitor Jin Woo closely. Although Woo No argues it was for research purposes, Jin Sung investigates deeper into the matter. As the investigation progresses further, Jung Woo No becomes more questionable. With increasing evidence pointing to Jung Woo No as the main suspect, the concealed truth becomes increasingly evident.

As the investigation into Jin Woo's death progresses, the case becomes increasingly clear. However, with his family and friends being involved in the case, Young Woon's resolve begins to waver. His family, friends, and even his memories challenge his choices. As the investigation team clashes with Jinjin Group, the time has come for Young Woon to pick his side.

Marie admits that Park Ki Young initially approached her with evidence of Jin Woo’s murder, prompting the investigation team to delve into Park Ki Young’s past. They question a friend of Ki Young’s mother and uncover new information. However, due to Marie’s change in stance, Director Yoo becomes aware of a traitor leaking information nearby. (Source: Viu)

Although Director Yoo uses her influence to wiggle out of the case, the special task force arrests Jung Woo No and Director Yoo to bring them in for questioning. Even though the special task force has gathered numerous pieces of evidence, Prosecutor Ko must carefully plan her move during the interrogation to wrap up this case.

Director Yoo and Jung Woo No stand in court as the defendants. Prosecutor Ko is missing the decisive evidence. Jung Woo No admits to abducting and locking up Ki Young but claims Jin Woo's case was not a premeditated murder. Director Yoo denies any involvement in the crime. Will Prosecutor Ko achieve justice?

Young Ju carries out the interrogation with Bae Min Gyu, the victim's husband, but there is no solid evidence of the crime. Furthermore, his lover, Lee Eun Byeol submits a new alibi for him, and he gets released once again. Meanwhile, another hideous murder case occurs with a similar display.