One of six great demon lords is slowly awakening from deep slumber, and if he does, there will be hell on Earth. It might be Cthulhu, or Shub-Niggurath, but most players won't know the identity of the hidden card until the endgame. This is important because each of the six tomes is best against a specific demon lord, middling against most of the others, and worthless against another specific one. Players are different teams of adventurers in the 1920s, finding tomes like the Necronomicon, fighting monsters like the Mi-Go, and solving world-spanning Events, mysteries of Lovecraftian weirdness. Events give victory points to whoever finally solves them, but the great demon will arise if there are 100 points worth of these Events in the unsolved stack--if he arises, there is the endgame of final apocalyptic battle. So players are constantly balancing co-operation with competition--under certain circumstances, a player can discover the great demon ahead of the endgame, and even decide to join the demon!