Donnie Yen plays a cop who has unconventional ways of enforcing the law, but once people he loves dearly are killed and he sees the maniacs he must stop, he will use brutal grappling techniques and devastating martial arts to bring their brutal reign to an end.
After filming, Colin Chou said it would be his last HK martial arts film because he says the people in the film industry there work very long hours, and they do everything completely real, and his body was getting beaten up.
Donnie Yen extensively studied techniques and styles used by MMA and UFC such as jiu-jitsu because he wanted a style rooted in grappling techniques as most HK martial arts films do not feature those kinds of styles.
Various fighting hits throughout the film are real hits. Usually when recording a fight scene, they always get close but never hit each other, but in this film, various punches and kicks are actually real. Many of these are slowed down and can actually be seen as not being faked.