Vin Diesel plays a narcotics undercover agent (called Sean Vetter) trying to stem the drug pipeline along the US/Mexican border. As one drug baron is arrested a mysterious figure, known only as Diablo, emerges on the scene. When Diablo murders Vetter's wife, the pursuit of Diablo becomes a personal vendetta. He loses his moral bearings and risks the lives of his fellow agents in a quest for revenge. Epic violent action sequences are interspersed with introspection and self doubt.