Catherine Fisher 
Snow-walker [EPUB ebook] 

Since Gudrun came from the frozen mists beyond the edge of the world, the Jarl’s people have obeyed her in hatred andterror. But the enchantress has one weakness: a son, Kari, banished to a forbidding fortress in the north, never seen by the Jarl’s people. In secret they wonder: Are the rumors true? Was he born a monster?Now Jessa and her cousin Thorkil have been exiled to the north, and if they survive the journey, they will find the truth: Is Kari a beast? Or the means to stop the sorceress?