Legends and worlds collide in a reimagining of folklore from the Scottish Highlands In Caithness, in the time of faeries, Sysa Steel lives a secluded life with Grey, her grandfather. That all changes when Grey takes Sysa to a faerie mound and she disappears into a strange, mysterious world. Once there, Sysa discovers the truth about her family and a quest for vengeance that threatens their existence. Meeting Brodie and Lavellan complicates things, while answers seem to lie in the stories Grey told her as a child. With everything at stake, Sysa must challenge the force of the Castle of Thunder. In a world full of magic, is the power of stories the greatest power of all?