On Ely Island, the Normans are proclaiming their authority with the construction of a magnificent cathedral. When Morcar, fishing for eels nearby, is attacked, his cousin Lassair is sent to nurse him. Morcar tells Lassair a frightening tale of assassins in the dark and a brief vision of horror. Then the killers strike again, and, as the secret hidden within the walls of Ely Abbey claims more victims, Lassair is forced to face a challenge that she fears is far beyond her . . .