Sourcery

There was an eighth son of an eighth son. He was, quite naturally, a wizard. And there it should have ended. However (for reasons we'd better not go into), he had seven sons. And then he had an eighth son...a wizard squared...a source of magic... a Sourcerer. «Sourcery» sees the return of Rincewind and the luggage as the Discworld faces its greatest — and funniest — challenge yet.