Katla is a slave and daughter of a Christian woman captured in a Viking raid on Irish shores. Setting sail from Iceland with her master's household, she heads toward the distant promise of a new homestead in Greenland. Also on the ship is Thorbjorg the Seeress, a much maligned and persecuted healer and prophetess who is ever faithful to the call of her patron god, Odin.

Upon first arriving in Greenland, Katla is brutally raped by her master's son, Torvard. The child of this union is Bibrau: taciturn, reclusive, infused with the savagery of her conception and suspected by many to be a changeling. But the seeress Thorbjorg, following a vision from her god, takes Bibrau as her apprentice. The young girl becomes an adept at healing and Norse magic, but her bitterness perverts the wisdom Thorbjorg gives. As her power grows, Bibrau twists it to good or evil at her whim, inflicting her will on Thorbjorg's household, her mother and the tight-knit Greenland community.

The Thrall's Tale is a chronicle of love, hatred and revenge at a turning point in history when Christianity first penetrates the pagan Viking sphere. The schisms, alliances and sacrifices that result reflect the pain of a dying culture and the birth of a different world.