The "Expedition to the Ruins of Greyhawk" adventure puts the adventuring party on a quest into the depths of the Ruins of Castle Greyhawk to save the Free City from the forces of the foul demigod Iuz the Evil - the half-fiend son of the demon lord Graz'zt and the evil archmage Iggwilv. Iuz built a sinister empire that once held the northern lands of the Flanaess in fear and constantly threatened the surrounding kingdoms in an attempt to rule the entire world of Oerth.