During the 1960s-70s in Hong Kong, the police and triads were colluding with one another and in 1973, the Independent Commission Against Corruption (ICAC) was established to clean up the Corruption within the police force. When two hard-boiled ICAC investigators (Louis Koo, Gordon Lam) encounter number one drug lord Crippled Ho (Tony Leung Ka-fai) and Chief Chinese Detective Tsui Lok (Francis Ng), a confrontation between good and evil triggers.