Sixteen-year-old Emeline de Gournay has always dreamed of adventure. But as the only daughter of a wealthy Norman baron, she knows her future is to marry a stranger her parents have chosen for her and remain by his side as a dutiful wife and mother. That is, until the morning of her betrothal, when her younger brother is abducted by a terrifying, shapeshifting Elderwitch. To make things worse, her only hope of rescuing him is to join forces with Owain ap Hywel, a young Welsh half-Hazelwitch she is inexplicably drawn to... and the boy accused of her brother's kidnapping. As they journey from her home in the turbulent Welsh Marches to a world of fighting Treewitches and mythical beasts, Emeline comes to realise that rescuing her brother will not be enough. The only way for peace to be restored, in both her own world and the world of the Treewitches, is to destroy the Elderwitch for good.