Keung in Hon's triad, while Lau, Hon's police spy, handles a case for a young woman, Mary, his future fiancée, setting up the events of Infernal Affairs. Cast Anthony Wong as Wong Chi-shing (黃志誠), a police inspector who aims to take down the Ngai family triad. Eric Tsang as Hon Sam (韓琛), a member of Ngai's triad. Carina Lau as Mary, Hon Sam's wife. Francis Ng as Ngai Wing-hau (倪永孝), the boss of the Ngai family triad after his father's assassination. Edison Chen as Lau Kin-ming (劉健明), Hon Sam's mole in the police force. Shawn Yue as Chan Wing-yan (陳永仁), Ngai Wing-hau's half-brother and an undercover cop. Hu Jun as Luk Kai-cheung (陸啟昌), a police superintendent who is Wong's close friend and partner. Chapman To as "Silly" Keung (傻強), Chan's friend and fellow triad member. Roy Cheung as Law Kai-yin (羅繼賢), an undercover cop in the triad. Liu Kai-chi as Uncle John (三叔), a prominent triad member. Joe Cheung as Ngai Kwun (倪坤), the boss of the Ngai family triad and Ngai Wing-hau's father who was assassinated by Lau. Henry Fong as Gandhi (甘地), one of the Big Four. Peter Ngor as Negro (黑鬼), one of the Big Four. Arthur Wong as Kwok-wah (國華), one of the Big Four. Teddy Chan as Man-ching (文拯), one of the Big Four. Chiu Chung-yu as Mary, the girl Lau meets in the police station at the end of the film. Phorjeat Keanpetch as Sunny, the Thai drug lord who tried to kill Hon Sam. Ye Shipin as a socialite at the handover party Tay Ping Hui as Hung, lawyer for the Ngais Hui Kam-fung as the principal of the police cadet school Alexander Chan as Ngai Wing-yee (倪永義), Ngai Wing-hau's elder brother. Andrew Lin as Ngai Wing-chung (倪永忠), Ngai Wing-hau's younger brother. Kara Hui as Ngai Wing-tsz (倪永慈), Ngai Wing-hau's elder sister Wan Chi-keung as Superintendent Leung (梁Sir), Wong's superior. Chan Charoenwichai as Paul, the Thai drug dealer who became friends with Hon Sam. Kelly Fu as May, Chan's girlfriend Music The film's score was composed by Chan Kwong-wing. The theme song, Eternal Realm (長空; Changkong), was composed by Wong Ka-keung, lyrics provided by Wong and Yip Sai-wing, and performed by the band Beyond. Reception The film was highly anticipated prior to its release due to the success achieved by Infernal Affairs. However, the general response to the film was mixed. Box office