With its companion volume, The Book of the New Jerusalem, Fearful Symmetries gives the Keeper guidelines for building an improvised campaign with dangers drawn from English folklore and Mythos abomination. Four systems of magic are described, along with locations, threats, tomes, and characters. Use Fearful Symmetries to flesh out the struggle between the lurking horror, and the shrivelled good intentions of those who think such power can be contained, and controlled, by mere mortals (Pelgrane Press website).