Madwand by Roger Zelazny
Pol Detson, son of Lord Det of Rondoval, has come home. He is now a powerful sorceror of unsurpassed natural ability - in a world where the power of magic is the only kind that matters. But Pol is still an untrained talent, a 'MADWAND'. To take control of his powers, to rule in his father's place, he must survive arduous training and a fantastic initiation into the rites of sorcery. As friends, Pol has one dragon and one thief. As enemies he has the most powerful wizards of the land. And at least one of them wants him dead.