The year is 1143, the setting the beautiful Isle of Skye in medieval Scotland. Rhys MacAulaed is a handsome, powerful Gaelic warlord who often travels the countryside disguised as a commoner. During one of his excursions, he meets and falls in love with Gwen, a beautiful peasant maiden. Rhys decides to make Gwen his wife and lady, but he is coerced into entering a politically expedient union. With deep regret, Rhys marries Mahrea - a cold and distant Icelandic princess who, unbeknown to Rhys, has a dark and evil soul.
Gwen is reunited with Rhys when she becomes a nursemaid to his newborn daughter, and their passionate romance is rekindled. Mahrea, well versed in the dark arts, becomes aware of her husband's relationship with the nursemaid through supernatural channels. She becomes intent on revenge. Her malice takes an unnatural and terrifying form.
Rhys must ultimately face his destiny as he fights the greatest physical and emotional battle of his life, at the summit of his castle's soaring tower. Based loosely on an old Skye legend, Mistress combines the excitement of an engrossing adventure with a sizzling romance.