When young academic Terry Williams goes to a remote corner of the Scottish Highlands, she's simply intending to edit the letters of Catherine McCulloch, tortured and burnt as a witch in the seventeenth century. But then the body of a young woman is found on a local farm, dumped in the death pit amidst a pile of rotting pigs. She is Donna Fairhead, one of a nearby community of Wiccans - modern-day witches.

As the forensic excavation of the death pit throws up yet more horrors, Terry's work on the letters reveals that there may have been more to Catherine's death than anyone had ever imagined. And as the present-day death toll mounts, Terry realizes that the identity of the killer may also be part of a three-centuries-old mystery, a mystery whose next victim might well be herself...