Wang Wei (Tony Leung Ka-fai), a police officer, witnesses the murder of his father-in-law, a police commissioner, at the hands of an assassin. When the assassin attempts to escape, he is then killed by a car bomb. Wei and his partner later identify the assassin, but discover that he was a felon who was apparently executed in prison several months ago. Wei decides to go undercover in the prison by assaulting a group of gang members at a bar. While inside, he is immediately suspected of being a cop and is beaten in a prison-orchestrated fight, leaving him bloodied and bruised.