A detective takes on a murder case that was disguised as suicide and becomes obsessed with solving it. But his younger sister falls in love with a man that is somehow connected to the murder. The detective tries to push the two away from each other, because he knows the man isn't a good person but the young woman has sympathy for him.

Moo Jin-Hyuk (Jang Hyuk) was a popular detective who solved major cases, but after his wife was murdered by a serial killer his life spiraled down. He is filled with guilt that he was not able to protect his wife and he secretly looks for her killer. Meanwhile, Kang Kwon-Joo (Lee Ha-Na) graduated at police academy with top marks. She began to work at an emergency 112 call center. Working there, a brutal murder case takes place and her father/police sergeant went to the crime scene. Her father is killed there and Kwon-Joo hears what happened over the phone. Afterwards, she goes to the U.S. to study and comes back to Korea as a professional voice profiler. Detective Jin-Hyuk and Kang Kwon-Joo solve cases together. Chasing a serial killer responsible for the deaths of their family member.

The story of two fearless men who are willing to go through extreme lengths in their pursuit of a returning serial killer. To uncover the murderer's identity, the two are forced to look deeper than what the evidence seems to suggest.

Kang Yo Han (Ji Seong) is a judge. He has an aristocratic appearance and elegant taste. He punishes corrupt and greedy men with power. Kang Yo Han a secret. Jung Seon Ah (Kim Min-Jung) is an executive director of the Social Responsibility Foundation. She is smart and beautiful. She is also Kang Yo Han's enemy. Jung Seon Ah is involved with important people from various social circles like politics and economics. She has the power to control the country by using her relationships. Kim Ga On (Park Jin-young) is a rookie judge. He has experienced difficult times since his parents died when he was a child, but he was able to become a judge after expending great effort. Yoon Soo Hyeon (Park Gyuyoung) is a detective. She is Kim Ga On's long time friend and she chases after Kang Yo Han's secret.

A crime thriller drama based on a web novel of the same name that contains the field experience of Kwon Il Yong, Korea's No. 1 profiler.

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