Sinsegye (2013) - IMDb
www.imdb.com
Sinsegye: Directed by Park Hoon-jung. With Lee Jung-jae, Choi Min-sik, Hwang Jung-min, Park Sung-woong. An undercover cop finds it difficult to play both a cop and a goon.

An undercover cop has his loyalties tested when the boss of the corporate gang he’s spent years infiltrating dies.

If you enjoyed The Departed (2006) this a good movie to check out