Demon Lord of Karanda by David Eddings

David Eddings tells the story of King Garion's abducted infant son and his efforts to save him. Unfortunately, he and his friends are detained by the friendly, but determined Zakath, who refuses to let them leave. As a horde of demons ravage the Cities and a plague lets loose its terrors, Garion has little time left to reach his destination, or the kidnapper wins by default.