Snow Walker book by Catherine Fisher

From the frozen mists beyond the edge of the world comes Gudrun, the Snow-walker, to rule the Jarl's people through fear and sorcery. But the enchantress has one weakness -- her son, Kari, banished as a child to Thrasirshall, the forbidding fortress in the desolate, snowbound north. The people of the Jarl have never set eyes on Kari, but in secret they wonder: Are the rumors true? Was he born a monster? Now, two will discover the truth. Because their fathers were loyal to the rightful ruler, Gudrun has exiled Jessa and Thorkil . . . to Thrasirshall. The cousins wonder if they can survive the impossible trek to the ruined castle. And if they do, what will they find at the end of their journey? A beast? Or the means to stop Gudrun? In this spellbinding saga, a resourceful heroine and an unexpected hero must discover a way to free the Jarlshold from tyranny or lose it forever -- to the Snow-walker. Published By Harper Collins on 2004-08-17