Bitter Magic, inspired by the true story of Isobel Gowdie and her witchcraft confession, reveals a little-known corner of history-the lives of both pagan and Protestant women in the Scottish Reformation of the 1600s as witch trials and executions threatened their lives, values, and beliefs.

The story is told by Isobel herself and also by Margaret Hay, a fictionalized seventeen-year-old noble woman. When Margaret stumbles across Isobel one day, it seems as though Isobel is commanding the dolphins in the ocean to dance. Margaret is enchanted. She becomes interested in Isobel's magic, in fairies, and in herbal remedies; Isobel freely shares her knowledge. While Margaret worries that being around Isobel could be dangerous, she also respects Isobel's medical successes and comes to believe that acknowledging the efficacy of herbal remedies or believing in fairies does not challenge her Christianity.

But Isobel believes in more than cheery fairies and herbal medicine. She has dark wishes as well, unknown to most people. Isobel seeks vengeance against the local lord who executed her mother for witchcraft. More important, Isobel's trance experiences (or are they dreams?) lead her to confess to a wide range of sins, including consorting with the devil. Then, during her trial, Isobel names thirteen others, calling them all witches. To her great shock, Margaret hears her own name. Can her tutor, a Christian mystic named Katharine, save them?