When Father Diego Serra found a young boy named Twilight Grimm fighting vampires on the steps of Serra's church, the priest had no idea he and the boy would become a decade-long team fighting against the nightwalkers. Now, after years of relative peace between the vampires and the humans on the other side of Hallowed Heights, Grimm learns from the daughter of the vampire overlord that the undead are about to break the truce by breaching the wall in the middle of the city and assassinating its mayor and his family! Can they stop them before blood is flowing in the streets and chaos (or all Hell on earth) breaks out?