Inspired by the writings of H.P. Lovecraft, you and your fellow players represent investigators in the 1920s who instead of trying to stop the coming of Elder Gods, want to summon those otherworldly beings so that you can put a stop to them permanently. You start the game insane, and while your long-term goal is to shoot Cthulhu in the face, so to speak, at some point during the game you'll probably fail to mitigate your dice rolls properly and your insanity will cause you to do something terrible — or maybe advantageous. Hard to know for sure.