Whilst book five was slightly disappointing because of a distinct lack of raw connection with Cat and Bones, book six - One Grave at a Time - puts the series back on form. 
 Once again, Cat and Bones are up against yet another cunning enemy, this time in the form of Kramer - a powerful ghost, disillusioned writer of the historic Malleus Maleficarum, and cruel, twisted rapist and murderer. He has haunted the plane of the living for years, yet annually, on Halloween, he has the ability to cross over into a corporeal form, allowing for his centuries-old ritual of the torture and burning of women, under the archaic system of witch-hunting. 
 Of all of the villains in this series so far, I enjoyed reading this one the most - perhaps because of my own interests surrounding the witch trials and the unspeakable history of the crimes against those women. 
 Cat, as always, puts her own (undead) life on the line to hunt down this madman, in yet another lightning joyride from Jeaniene Frost.