Jennet is the daughter of the Witchfinder of Mercia and East Anglia. Whilst her father roams the countryside in search of heretics, Jennet is left behind to be schooled by her aunt Isobel in the New Philosophy principally expounded by Isaac Newton. But her aunt's style of scientific enquiry soon attracts the attention of the witchfinders. To save her aunt, Jennet travels to Cambridge to seek the help of Newton himself. Isobel is burned at the stake but in her dying moments, begs Jennet to devote her life to overturning the Parliamentary Witchcraft Act. This is a huge rollercoaster of a novel as Jennet travels to America and witnesses the Salem witch trials; is abducted by Indians; begins an affair with Benjamin Franklin; travels back to England and finally meets the real Newton; is shipwrecked; then ends up back in America where her brother is now the Witchfinder Royal. In a great final showdown between old superstition and new science, Jennet decides to have herself accused of witchcraft in order to disprove its existence.