As the Romans invade Britannia, the princess of the great tribe of the Brigantes watches the enemies of her people come ever closer. Cartimandua's world is a maelstrom of love, conflict, revenge, and retribution. Her life takes one unexpected turn after another as tragedy changes the course of her future.
In the present day, historian Viv Lloyd Rees has immersed herself in the legends surrounding the Celtic queen. She is writing a dramatisation of the young princess's life with the help of an actress, Pat Hebden. Viv's Head of Department, Hugh Graham, hounds her as she struggles to hide her visions of Cartimandua and her conviction that they are real. Her obsession grows ever more threatening, and both Pat and Hugh are drawn into the intrigue, as past envelops present and the trio find themselves facing the greatest danger of their lives.