A dark shadow grows in the city of Arkham. Unspeakable alien entities known as Ancient Ones lurk in the emptiness beyond space and time, writhing at the gates between worlds. These gates have begun to open, unleashing monsters and madness, and must be closed before the Ancient Ones make our world their ruined dominion.
Will the only organizations in Arkham with the power to prevent its impending demise collaborate to uproot those among them who have aligned themselves with the alien horrors? Or will suspicion and paranoia pave the way for the Ancient Ones to devour the world?