Equal Rites (Discworld #3, Witches #1)

Every world has its rules--even a flat onecarried by four elephants riding on a giant turtle. That's why a dying wizard is searching for an eighth son of an eighth son to bestow his wizardly powers upon before meeting Deathin six minutes. Unfortunately it is quicklydiscovered--though not quite quickly enough--that the newborn babe the wizard anoints just before bidding the Discworld adieu is, in reality, a girl! What's done cannot be undone--despiteold Granny Weatherwax's attempts to bringthe child into the witchy fold--and little Eskis now a wizard, through and through. And she's destined to bring chaos and confusion to the all-male faculty of Ankh-Morpork'sUnseen University . . . who are alreadyfairly addled to begin with.