Ireland, 1000 AD. Gormflaith is unhappily married to Brian Boru, High King of Ireland, and although a queen she struggles with her limited position. As an immortal Fomorian with the secret gift of magic, Gormflaith has a burning desire: to find and destroy the hidden fortress of her sworn enemies, the Descendants, who seek to kill her kind at all costs. She begins to use her magical powers, and discovers she is more skilled than she ever realised... but can she control what she will become?

Meanwhile Fódla, the Descendants' healer, mourns her banished sister but clings to life as the guardian of her young nephew. She seeks a place of safety for them both, but he has secrets of his own that could threaten everything – and Fódla must do all in her power to keep him hidden away from those who would use him for evil.

When a mysterious man comes to King Brian's court, his presence could spell disaster or deliverance for both Gormflaith and Fódla – and for Ireland herself. For he is Tomas, an ambitious immortal with few scruples – and he will do anything to see his plans become reality.

Soon, mortals and immortals alike are drawn towards a bitter conflict that could decide the future of Ireland and all her people.