In the 1990s, a police officer goes undercover to infiltrate a mega crime syndicate that distributes illegal drugs across South Korea, China and Japan. His wife, a narcotics officer, is also involved.

Park Jun-Mo (Ji Chang-Wook) is a police officer. For a drug investigation that leads into the drug trade between South Korea, China, and Japan, Park Joon-Mo infiltrates a criminal organization. Meanwhile, Park Jun-Mo is married to Yu Eui-Jeong (Lim Se-Mi). She is also a police officer and becomes involved in the drug investigation that her husband is working on. Appearing by them is Jung Gi-Cheul (Wi Ha-Joon). He is the charismatic boss of a newly formed crime organization.—AsianWiki

Set in Seoul in the 1990s, a former DJ starts selling a new powerful drug nicknamed "Gangnam Crystal" in city nightclubs after mastering a gangster organization. Since the police know little about the origin of such drugs, in order to crack down on this rampant drug trafficking organization, rural police officer Park Jun Mu is assigned to sneak into the organization, only to discover that his wife, Yoo Eui Jung , also a detective, has volunteered to participate in this dangerous mission and seems to have an unspeakable past with the heinous underground drug king. Park Jun Mu in this drug-related mission, not only does he wholeheartedly fight the drug cartel, but also works hard to protect his wife's safety at all times.—MyDramaList