Undercover cops posing as triad gangsters have been staple figures in HK cinema since Alex Cheung's Man on the Brink (1980, sort-of remade by Andrew Lau in 1994 as To Live and Die in Tsimshatsui), but this huge domestic hit goes one better by twinning its fake triad cop (Leung) with a triad mole in the police force (Lau). Each mole is answerable to the other's nominal boss (Wong and Tsang respectively), leading to tactical complications and a lot of genuine suspense as each side tries to outwit the other over a shipment of dope from Thailand. There's no hint of an auteur sensibility at play, but the careful plotting, rich characterisations and sleek mise-en-scène give this an impact rarely seen in HK films these days. Leung is outstanding as a man close to mental and physical breakdown, and Lau's cocky narcissism is exploited more cunningly than usual. The Chinese title invokes the lowest circle of Buddhist hell, a fair indication of how noir things get.