Parthoris is the fictional world depicted in Heretic. It is noted as the home of the elvish Sidhe race, of whom Corvus, the protagonist of Heretic, is a member. Parthoris was invaded by the Serpent Riders, who corrupted the other races of Parthoris into their service and turned them against the Sidhe. When attacked, the Sidhe elders blew out their mystic candles, destroying the armies of the Seven Nations. This caused D'Sparil, the lone Serpent Rider left behind to rule Parthoris until its doom, to retaliate with genocidal warfare.