The Divided Isle, once a place of peace and tranquility, has been ravaged by war. Twins Oona and Morris live quietly with their grandmother in the south, but the threat of the Invaders of the Black North—the ravaged northern part of the island—is coming ever closer. When Morris is kidnapped by one of the evil Briar Witches, Oona must journey to the Black North in search of her him, accompanied only by a jackdaw with mysterious powers, and a treasured secret stone which the Invaders want more than anything.