A vicious killer, Feng, is going round Hong Kong killing martial arts exponents, leaving a secret weapon called the Moonshadow as his calling card. When convicted murderer and kung fu expert, Ha Hou Mo (Donnie Yen) hears of this he offers to help the police catch the killer, in return for his freedom. Despite their misgivings, the police release the condemned criminal into their custody. With his help they uncover the killer's murderous pattern - he is targeting and killing his victims using their own practise of martial arts training. Will Ha be forced to go against his own martial code in order save a city plunged into fear?