Working in New York's "Asian Gang Unit", Nick Chen's (Chow Yun-Fat) job is to keep the violence and strife of the Chinese gangs from spilling out into the streets. Although long years of experience have taught him that the gangs can never be wiped out, only suppressed, he has recently been joined by a junior partner, Danny Wallace (Mark Wahlberg). Wallace has a much more idealistic view of his job, seeking to help people and "make a difference". While the two partners work together, they each have secrets they conceal from the other. While Chen is perhaps a little too friendly with some of the gangs, Wallace is plagued by a gambling-addicted father constantly looking for hand-outs. After loansharks threaten his father, Wallace is approached by one of the gang leaders, offering cash in exchange for police favors. Wallace quickly learns that the sway of dirty money is difficult to resist, but in taking it, he may be risking more than just his ideals.