Moonlighting

In a sleepy rural village, the local piano academy is a picture of peace...until the sun sets. Seonwu Jin is the academy's exhausted instructor, living as the "wife" of the charismatic village head, Goh Hui-jae. But the domestic bliss is a deadly front. Jin is an undercover cop on a high-stakes surveillance mission, and Hui-jae is the ruthless mob boss who vanished after a bloody power struggle. By day, Jin plays the perfect partner; by night, he does power to ensure he isn't made. But as the organization closes in, the lines between his cover and the truth begin to bleed.

(Source: Lezhin Entertainment)