Ma Jun (Donnie Yen), a sergeant in the crime squad, is dedicated to catching criminals. He is very skilled and often overreacts because he is eager to catch thieves. The police have been collecting evidence of the crimes of the Vietnamese gang brothers Ah Zha (Ray Lui), Tony (Collin Chou), and Ah Hu (Hsing Yu), so they sent Watson (Louis Koo) to infiltrate them as an undercover agent. The three brothers are ruthless and want to eliminate Ah Shan, the thorn in their side. After Ah Zha was arrested, Tony also saw through Watson's true identity and wanted to kill Watson and other witnesses to rescue his eldest brother. Watson's girlfriend Qiu Di (Fan Bingbing) was held hostage, and Watson had to give up testifying against Ah Zha. Watson and his girlfriend were taken hostage, and Ma Jun also took Ah Zha to rescue Watson.