Undercover (2007)

Feng (Shawn Yue) is a former undercover cop whose post-assignment life has begun to rapidly disintegrate. Feng and former triad brother Fai (Sam Lee of Gen-X Cops) are caught using cocaine, and the ensuing melee leaves a police detective dead, with Fai fingered as the culprit. Fai must go on the run, but he no longer trusts Feng, who he believes may be leveraging their brotherhood for advancement in the police ranks.