Serpent Mage - Margaret Weis, Tracy Hickman

After the four worlds Alfred has at last found  his people on Chelstra, the realm of sea. But his  travels have taught him to be cautious... and  Alfred soon realizes his caution is justified, even  among his own kind. The one person Alfred can trust  is, strangely, Haplo the Patryn. But Haplo's lord  has decreed all Sartan to be the enemy, and Haplo  dares not go against his lord. Now the companions  have arrived in a land where humans, elves, and  dwarves have learned to live in peace. Unaware of an  even greater threat to all the realms, it is  Sartan and Patryn who will disrupt this alliance of the  lesser races in their struggle to gain control of  all four worlds. Only Alfred and Haplo realize  that they have a much older -- and more powerful --  enemy than each other...