In the spring of 1688, Walter Stearne, Witchfinder-General for Mercia and East Anglia, roams the countryside in search of heretics. His daughter Jennet is left behind in the care of her Aunt Isobel, who schools her in the New Philosophy expounded by Isaac Newton. But her aunt's style of scientific enquiry soon attracts the attention of the witchfinders. Jennet's attempts to save her aunt are ultimately doomed, but she promises Isobel that she will devote her life to overturning the Parliamentary Witchcraft Act. The heroine's quest will entail many picaresque adventures, including a brush with the Salem Witch Trails, a Caribbean shipwreck, and a final showdown between the old superstition and the new science.