Belgariad 4: Castle of Wizardry (Penguin Random House Children's UK)

Garion and his companions now have the Orb of Aldur, carried by an innocent young boy, and must return it to its rightful home on the pommel of the sword in the Great Hall on the island of Riva. As they journey across the lands, Murgo soldiers and Grolim sorcerers try to stop them. But Garion's true adversary, the evil God Torak - is waking up in his dark tomb - ready for the final conflict.