Once upon a time on the Disc, the eight son of an eight son (eighth sons all become wizards, because magic on the Disc follows the rule of eights) had seven sons. And then he had another son, who was destined to be the most powerful wizard of his time: a source of magic. A sourceror, if you will. He was guided by his magic staff, which, naturally, was possessed by the spirit of his dead father.
This book is not about the sourcerer. Terry Prachett only bothers to keep us updated on the movements of the sourcerer (a boy called Coin) when there's no other way around it. This is a book about Rincewind the wizard, which means that our protagonist spends the majority of his time hiding, if not actively running away, from the plot of his own book. For anyone reading this book with no prior knowledge of Discworld, this will make him a confusing and frustrating protagonist. If, however, you're like me and adore him with all your heart, you will be delighted.
Honestly though, how can you not be delighted by a hero who's faced with a blatant Call To Adventure and reacts like this:
"A thing with a goblin's face, harpy's body and hen's legs turned its head in a series of little jerks and spoke in a voice like the peristalsis of mountains (although the deep resonant effect was rather spoiled because, of course, it couldn't close its mouth).
It said: 'A Ourceror is umming! Eee orr ife!'
Rincewind said "Pardon?" But the thing had gone past and was lurching awkwardly across the ancient lawn.
So Rincewind sat and stared blankly at nothing much for fully ten seconds before giving a little scream and running as fast as he could."
The whole book is endlessly quotable, honestly, and also I'm kind of at a loss to describe the plot in any more detail, so here are some more quotes I bookmarked while I was reading:
"This happens to everyone sooner or later.
For example, in a tavern someone jogs your elbow and you turn around quickly and give a mouthful of abuse to, you become slowly aware, the belt buckle of a man who, it turns out, was probably hewn rather than born.
...In other words, it's the familiar hot sinking feeling experienced by everyone who has let the waves of their own anger throw them far up on the beach of retribution, leaving them, in the poetic language of the everyday, up shit creek."
"'I can't hear anything,' said Nijel loudlly. Nijel was one of those people who, if you say 'don't look now,' would immediately swivel his head like an owl on a turntable. These are the same people who, when you point out, say, an unusual crocus just beside them, turn around aimlessly and put their foot down with a sad little squashy noise. If they were lost in a trackless desert you could find them by putting down, somewhere on the sand, something small and fragile like a valuable old mug that had been in your family for generations, and then hurrying back as soon as you heard the crash.
Anyway."