In the land of Ytir, the Ard Ri, ruler of all the Great Families, is preparing for war. To invade the Duchies across the great river, he needs the services of a powerful yspridwch - but the young girl he was going to use has been kidnapped by one of his own Harpers.
Traitor to his own people, Malcolm Petroc is hiding out in a parallel world, working as a bookseller in Hay-on-Wye, and Branwen is growing up without any interest in the world she came from.
Now Mal's ex-wife has tracked them down, and sends Arian, their daughter, to bring them back. Convinced of the rightness of the Ard Ri's cause at first, Arian discovers the truth is more complicated than she thought, and she has to choose where her loyalties lie.
Ytir will descend into chaos because of the Ard Ri's obsession - and Branwen needs to learn how to use her magical powers fast, to keep the people she loves safe, and to find a way to get home.