In 1991, Ni Kun, the leader of the Hong Kong gang, was killed. Among the five major leaders of the Ni family, except Han Chen (Zeng Zhiwei), they all waited for an opportunity to betray and attack. Unexpectedly, they were restrained by the inconspicuous second-generation Ni Yongxiao (Wu Zhenyu), the Ni family, without any effort. This move attracted the vigilance of the serious case inspector Huang Zhicheng (April Wong), and caused him to send a police academy student Chen Yongren (Shawn Shawn) to infiltrate the Ni family for a long undercover work. In order to consolidate his power, Han Chen installed an informant Liu Jianming (Edison Chen) in the police.Three years later, Ni Yongxiao, whose career is booming, decided to wipe out the five major leaders in one fell swoop, but because of negligence, Han Chen became a fish that missed the net.In 1997, Han Chen, who survived the disaster, resurrected the world. In order to avenge his dead colleagues, Huang Zhicheng found him to discuss cooperation to get rid of Ni Yongxiao, but soon found that this move had made a big mistake. Chen Yongren and Liu Jianming, who were both worried about their embarrassing identities, were walking further and further on the road of infernal Affairs.