The teenage Luned left her farm with the dream of becoming a scholar-nun on Tintagel. Her hard-won success is now thrown into danger by the arrival of a bitter nine-year-old. Accused of trying to kill her baby brother Arthur, Morgan is imprisoned on this island nunnery. Luned is appointed her guardian.

The Abbess Bryvyth battles for Morgan's soul. But Tintagel is visited secretly by Morgan's nurse Gwennol, a wise woman of the Old Religion. Luned herself is endangered as she is caught up in the struggle between them. She is coming ever more surely under Morgan's power.

As she grows towards womanhood, Morgan must decide how to use that power.