After defeating a second incursion of Hastur's cult under Castle Brytha in Meawold, preventing the kingdom from falling under his control, the party members find themselves drawn into Hastur's Domain: Carcosa. With twenty-four hours to escape before they become a permanent part of the domain, the party members must navigate the foreign land and find a way home. Four demon lords, three brothers, and the demonic seductress they all worship, control Carcosa. Perhaps one or more of them can be manipulated to help get the party home.