During the medieval period, Jason o' the Blood, a knight serving King Arthur at Camelot, suffers a near-fatal injury inflicted by Morgaine Le Fay. To save his life, the wizard Merlin intertwines the souls of Jason and Etrigan, a demon from the Underworld. This act not only revives Jason but also grants him numerous abilities, including immortality. Fast forward several centuries, Jason Blood has become a demonologist in Gotham City, where he and Etrigan are summoned by an old acquaintance to confront their former adversary, Morgaine Le Fay, who has returned with ambitions of world domination.
