Estranged from his children after the death of their mother, hardened homicide detective Aiden Breslin (Dennis Quaid) is called in to investigate a series of ritualistic murders. His search brings him into contact with Kristen Spitz (Zhang Ziyi) the daughter of one of the victims. She pleads with him to find the killers, but then, five minutes later, reveals herself to be one. She explains that she is part of a group who model themselves after the four horsemen of the apocalypse (War, Famine, Pestilence and Death), and that there will be more murders. And, well, shit gets crazy from there.