Set in the world of Cthulhu: Death May Die, in a period in which the Great Depression rages across most cities of the United States, cultists explore the nation's vulnerability, seeking to remake it into a twisted version of itself by consorting with unspeakable beings from nightmarish dimensions. Investigators take the opposite side, standing against this dark providence.

Players are secretly divided onto both sides of this conflict and use their influence to bid for the right to claim assets, take control of cities, and consort with powerful Mythos. Trying to keep their identity secret and avoiding insanity, players perform a multitude of actions, swaying agents to their side, assassinating rival agents, blocking opponents from performing actions, and sealing or protecting gates to otherworldly dimensions, among others to progress their agenda and score points. Although players are divided into opposing sides, this is not a team game. Only the player with the highest score of the leading side in the battle will claim victory and change the destiny of the nation.