The series follows Moo Jin-Hyuk (Jang Hyuk) and Kang Kwon-Joo (Lee Ha-Na) as they attempt to catch a serial killer who is murdering close family members. Jang Hyuk portrays Moo Jin-Hyuk, a former star detective whose character has gained great fame for solving cases. However, his world shatters when his wife is killed by a serial killer. He blames himself for not being able to protect her and begins searching for her murderer. Lee Ha-Na plays Kang Kwon-Joo, a professional voice profiler. Her character graduated at the top of her class from the police academy. One day, while working at the 112 call center, she witnesses her police commissioner father being murdered by a killer over the phone. Following this traumatic event, she goes to America to study and returns to Korea as a professional voice profiler. Together with Moo Jin-Hyuk (Jang Hyuk), she pursues the killer.
