The Iron Ring — Lloyd Alexander

When Tamar, the young king of Sundari, loses a dice game, he loses everything--his kingdom, its riches, and even the right to call his life his own. His bondage is symbolized by the iron ring that appears mysteriously on his finger. To Tamar, born to the warrior caste, honor is everything. So he sets out on a journey to make good on his debt--and even to give up his life if necessary. And that journey leads him into a world of magic, where animals can talk, the foolish are surprisingly wise, and danger awaits...