Castle of Wizardry

The Orb of Aldur has been retrieved, but Garion's journey is not over yet. He and the rest of the questers must escape the collapsing remains of Ctuchik's tower, burdened by an unconscious Belgarath and an innocent little boy carrying the world's most powerful magical item. Then they must journey to Riva to return the orb to its rightful place to await the Rivan King... but who could that be? And why does the orb keep singing to Garion, and rifling through his memories?