In World War Two, Oxford academic Dr Iana Jenkins discovers an unknown medieval chronicle by the nun Mary of Shaftesbury.

Mary confides that she was at Glastonbury Abbey in 1191 when its monks exhumed the bodies of King Arthur and Queen Guinevere. However, the great abbey's celebrations turn to terror when the mortal remains of Arthur and Guinevere turn out to be not what they seem, and horror reigns.

When all else fails, can Wulfrun - a priestess of the Old Religion from the forest - save the abbey from what has been unleashed.