Discworld 05: Sourcery

'It's vital to remember who you really are . . . it isn't a good idea to rely on other people or things to do it for you, you see. They always get it wrong.'
An eighth son of an eighth son is born, a wizard squared, a source of magic. A sourcerer.
Unseen University, the Discworld's most magical establishment, has finally got its wish: the emergence of a wizard more powerful than ever before. You'd think they would have been a little more careful what they wished for . . .
As the sourcerer takes over the University and sets his sights on the rest of the world, only one wizard manages to escape his influence. Unfortunately for everyone, it's Rincewind.
Once again the cowardly wizard must embark on a quest: to deliver a precious artefact - the very embodiment of magic itself - halfway across the Disc to safety. If he doesn't make it, the death of all wizardry is at hand.
And the end of the world, depending on who you listen to.