Iseult is a British shadow queen from Cornwall who appears in The Pale Horseman. Iseult was married to a minor king named Peredur who kept her virginity in the belief that it maintained her powers of prophecy. Seeing that Uhtred's arrival would result in her freedom, she convinced Peredur to hire on Uhtred and his ship's crew when they appeared off the coast in order to fight the Danish warlord Svein of the White Horse, who had captured a nearby fort. Svein and Uhtred ended up colluding to turn on Peredur and pillage his settlement, and Uhtred claimed Iseult and began living with her although he was still married to Mildrith.
Although Iseult healed Alfred's son Edward from an illness that nearly killed him and created herbal medicines for Alfred that made him healthier, she was feared and distrusted by the Wessex court because of her paganism. Alfred used her as a "surety" to ensure that Uhtred would not betray him and go to the Danes. She was later baptized, which helped alleviate some of the resentment against her. She prophecised that Uhtred would father three children, two sons and a daughter but refused to go into any detail when pressed. She was killed during the Battle of Ethandun when the Danes attacked the Wessex caravan behind their line. She was beheaded by Skorpa and presented to Uhtred. Who raged and killed Skorpa. She was then attached with her body and given a burial.
- Iseult is a native of Kernow or Cornwalum (modern Cornwall). And as a 'shadow queen' is one of the remaining Celtic pagans in Britain.