The balance between good and evil currently sits heavily in favor of good, which is precisely the problem. A succubus and her twin brother — an incubus — decide to do something about it. The plan: fight their way out of hell, deal with some humans and cathedrals along the way, and then take the conflict directly to the angels responsible for the imbalance. The goal is not domination. The goal is a more equitable arrangement between realms.