During the time Hong Kong was under British rule, there was a dark age when corruption and bribery were the order of the day. Chinese Chief Inspector Lak (Tony Leung Ka-fai) together with his gang, Unicorn (Anthony Wong), Gale (Eason Chan) and Gold (Wong Jing) laundered massive sums thereby making Hong Kong an empire of graft. Whenever they failed to apprehend the felons, Unicorn would get innocent victims, like Bong (Alex Fong), to admit to the crimes. Gale had nine "wives", all of them were actually mistresses of other constables, only Lily (Kate Tsui) was loyal to him, but Gale was fascinated by the female drug lord, Rose (Liu Yang). Lak was found having an affair with Unicorn's mistress (Natalie Meng Yao). Unicorn beat up Lak and was demoted to stand guard at a reservoir. In the early 1970s, the Governor of Hong Kong decided to clean up the police force. The ICAC was established, whose operation branch was headed by Yim (Bowie Lam). Bong and Unicorn also joined the ICAC. Despite threats of violence and intimidation, they managed to bring about the downfall of the empire of graft.
