The Lady Apollonia of Aust, medieval sleuth and wealthy daughter of an earl, faces widowhood for the third time. She chooses to guarantee her sovereignty by vowing to become a Bride of Christ, declaring that she will live a nun's life but remain in the world. Her household takes up residence in Cirencester. There they encounter an ongoing power struggle between the local Augustinian Abbey and the townspeople. After centuries of the abbot's declaration of being lord of the manor, the people of Cirencester search for ways to stop the abbey's abuses of power against the town. Upon her arrival the Lady learns that, in the absence of the abbot, the abbey is being run by its prior, an evil living canon. He is known to abuse his power as a manipulative predator without a shred of human compassion or call to Christian ministry. Lady Apollonia is not only forced to deal with murder, she finds herself under attack by one whose muddled mind regards her as the source of evil.