When historian Diana Bishop opens an alchemical manuscript in the Bodleian Library, it's an unwelcome intrusion of magic into her carefully ordered life. Though Diana is a witch of impeccable lineage, the violent death of her parents while she was still a child convinced her that human fear is more potent than any witchcraft. Now Diana has unwittingly exposed herself to a world she's kept at bay for years; one of powerful witches, creative, destructive daemons and long-lived vampires.

Sensing the significance of Diana's discovery, the creatures gather in Oxford, among them the enigmatic Matthew Clairmont, a vampire geneticist.

Diana is inexplicably drawn to Matthew and, in a shadowy world of half-truths and old enmities, ties herself to him without fully understanding the ancient line they are crossing. As they begin to unlock the secrets of the manuscript and their feelings for each other deepen, so the fragile balance of peace unravels...