On the Edge (2006)

(Cantonese with English subtitles) After 8 years of working undercover among Hong Kong's notorious triads, Harry Sin busts a crime lord and returns to regular police work. But old habits die hard, and Harry's immersion in the underworld is tough to shake. When his new partner decides to snub him, the only way out for Harry may be the dangerous life that has consumed him for nearly a decade.