The Tiger's Eye (Book 1 of the Angus the Mage Series)

Angus wakes up one day with a problem: his memory is gone. He doesn't know who he is or what he does. Voltari tells him he is his apprentice, but Angus knows nothing about magic. Still, Voltari is a Master Wizard, so he would know, wouldn't he? Voltari knows other things about him, too, but he isn't talking. Then, just as Angus begins to come to terms with his situation, everything changes....