Action thriller written and directed by Teddy Chan. Former martial arts instructor and current prisoner Ha Hou-Mou (Donnie Yen) offers to help the police force in their hunt for a mysterious serial killer targeting martial arts masters and quickly surmises that the killer is working his way through masters who he believes are weaker than himself. Ha returns home to learn more of the secret weapon known as the moon shadow which is being left at the crime scenes by the suspect, an action that makes the police believe he is in league with the killer. Meanwhile, things get even worse for Ha when the woman he loves is targeted, forcing him to make some difficult decisions about his relationship with the martial arts code.