Told through an assortment of letters, diary entries and clippings, Katherine Kramer falls ill after cutting herself on a strange book. Despite a desperate attempt to save her by her husband Richard, a professor of medicine, and his friend and colleague Charlie Bentwith, Katherine dies in horrific circumstances.

When Charlie's wife Constance falls ill in similar circumstances, the two friends are plunged into a murky underground world of witchcraft and esoterica, far removed from the science they know and trust. With the London press wondering whether the Ripper has returned, the friends must race against time to save Constance and avenge Katherine's death.