Choi Kwang Il

In 1999, a recording tape containing a mysterious serial murder and an eerie sound is discovered in a rural town. In 1987, terrorist Jo Gyeong Ho released sarin gas at a train station, killing passengers before turning himself in. His daughter, Jo Jae Yeong, was sent to live with his younger sister, Jo Jeong Hyeon. A decade later, Detective Choi Hyeong investigates a murder case he suspects is linked to the past attack. When Jeong Hyeon's niece goes missing, she joins Choi Hyeong to uncover the truth and save her. (Source: MyDramaList)

A series of disappearances take place in Gangnam, Seoul. Jae Hui works for a famous bar in Gangnam and she knows a secret involving the series of disappearances, but she also disappears. People who become involved with the case include Detective Kang Dong U, who was demoted and then returned to work, Gangnam outlaw Yun Gil Ho, who put himself on the list of suspects, and Prosecutor Min Seo Jin, who works on this case as an opportunity to raise her status. They chase after the truth of the case for different reasons. (Source: AsianWiki)