Baek Hee Sung and Cha Ji Won are a married couple with a daughter. Ji Won received an unpleasant relationship with Hee Sung's parents despite being together. Ji Won is a detective and investigating a case in which In Seo, a boy, got into an accident and pointed his father as the culprit. It's between their family issue as the boy witnessed a heart-wrenching sight of his father with another woman. 18 years ago, a murder case occurred where Baek Hee Sung lives as Do Hyun Soo. He was a suspect. Now, Reporter Kim Moo Jin unexpectedly met him in Hee Sung's Metal Craft Workshop without knowing his current identity. Hee Sung strangled Moo Jin and hid in the basement. Ji Won, the wife, has no clue about his husband's doings.
A murder case similar to the Yeonju City serial murder case happens. The victim’s thumbnail was missing, and she had a noose around her neck. Something seems off about the case and Ji Won tries to solve it. Meanwhile, Hee Seong finds out that Moo Jin had a plan to meet his informant, Soon Kil to get a tip. And Hee Seong decides to do something about it.
Ji Won feels something is not right when she saw Hee Seong coming home with a raincoat on in the middle of the night. The next day, Ji Won gets assigned another murder case and the surveillance footage shows that the victim got killed by a man in a raincoat. And all the evidence left at the crime scene points Do Hyun Su as the prime suspect.
Hee Seong gets baffled to become the prime suspect of Hoesin-dong Chinese restaurant murder case. Only Hee Seong and Moo Jin know that someone else is copying Do Hyun Su to pin the murder case on him. And Hee Seong and Moo Jin decide to work together to find out the person while Ji Won meets Do Hae Su, Do Hyun Su’s sister, to find more about the suspect.
A police officer hands over a watch strap as a piece of evidence from the crime scene in Gakyeongri to Ji Won. It is the strap that is engraved with Hee Seong’s initial on it. Ji Won instinctively feels something is wrong. And the owner of the inn calls the police to report that a taxi driver is beating up a passenger. Ji Won realizes that Hee Seong is somehow involved in the case.
Hee Seong was brought to an emergency room without any consciousness. Luckily, he wakes up, but Ji Won heard something unexpected while Hee Seong was unconscious.
Ji Won can’t clear up her doubts about Hee Seong, so she triggers him with the recording of Do Hyun Su’s voice and asks him to go to Do Min Seok’s workshop. When Hee Seong gets to the workshop, he panics and asks Ji Won to leave. Meanwhile, Hae Su meets up with Moo Jin and tells him that Do Hyun Su isn’t the actual accomplice.
Hyun Su asks Moo Jin to look for Hae Su in order to find the accomplice. During a stakeout, Ji Won encounters In Seo from an earlier case. Ji Won’s team gets to reinvestigate the Yeonju City serial murder. Meanwhile, Hyun Su finally meets Hae Su, and the three of them get together to find the accomplice.
Ji Won visits Moo Jin’s house and finds Hyun Su and Hae Su there. Hyun Su hurriedly tells Ji Won that he was helping Moo Jin’s investigation, but Ji Won gets more certain that her husband is Do Hyun Su. She ends up telling him that she doesn’t love him anymore. Hyun Su thinks the only way to turn things back to normal is to find the accomplice himself.
Hyun Su seals a deal with the human-trafficking ring run by Yeom Sang Cheol. His goal is to save the kid and retrieve information about Do Min Seok’s accomplice. He calls the police for backup in agreement for the big case. However, Ji Won feels anxious about Hee Seong’s every move and Hee Seong starts to think that Ji Won might know who he really is.
Knowing that Detective Choi found out about Hyun Su’s identity, Ji Won begs him to turn a blind eye on the case. Meanwhile, Hyun Su gets into trouble while undergoing a plan to find Do Min Seok’s accomplice.