Inspector Michael Wong (Simon Yam), alongside Shirley Ho (Carol Cheng), Brother Lung (Bryan Leung), Fan Chun-yau (Jacky Cheung), Uncle Tat (Ng Man-tat) and Terry (Donnie Yen) are all part of the Anti-Drug Unit of the Royal Hong Kong Police Force. The relationship between them are like brothers in general. During an operation, they worked together to bust a drug den but the chief drug trafficker, Swatow Hung (Wang Lung-wei), escaped. Just as they were celebrating their success, Hung found them and killed Lung. In order to avenge Lung and find Hung, they took a variety of means and finally found and killed Hung. During an accident, Yau filmed Tat trading with a drug trafficker and tells Terry and Michael. After Michael found out, in order to protect himself, he killed Terry and framed Yau, who was then suspended from duty, which caused Yau to suspect something fishy. One day, Yau's girlfriend, Amy (Irene Wan,) found a videotape at home and discovered that Michael and Tat were accomplices, but in order to save Yau, she handed the tape to Michael, which also led to her fatal demise. At this point, Yau and Shirley discover the truth to everything, that Hung luckily escaped from the drug bust earlier and came back to revenge on Lung, who was an undercover cop, on the night before his wedding with Shirley. Yau vows to bring the perpetrator to justice and dig out the mole inside the police force. Terry, who was partners with Tat, discovered his relationship with the drug traffickers and conflicted for his loyalty to Tat or his ethnic standards. Tat was used by his superior Michael and was ultimately abandoned and killed. Shirley finally discovers the truth to the case, but now, it is difficult for all of them to escape death.