Way out in the furthest part of the known world, a tiny stronghold exists all on its own, cut off from the rest of human-kin by monsters that lurk beneath the Snow Sea. There, a little boy called Ash waits for the return of his parents, singing a forbidden lullaby to remind him of them - and doing his best to avoid his very, very grumpy yeti guardian, Tobu. But life is about to get a whole lot more crazy-adventurous for Ash. When a brave rescue attempt reveals he has amazing magical powers, he's whisked aboard the Frostheart, a sleigh packed full of daring explorers who could use his help. But can they help him find his family?