"Sourcery" is the fifth novel in Terry Pratchett's hugely popular Discworld series, was first published in 1988 and is the third to give a starring role to Rincewind, the cowardly one-spell wizard.
Wizardry is widely seen as the most appropriate profession for the eighth son of an eighth son - however, given that it's also a celibate profession, is isn't a job that is intended to run in the family. Unfortunately, accidents do occasionally happen and the eighth son of a wizard is known as a Soucerer - a wizard who is also a source of magic. They are hugely dangerous, and will increase the background levels of magic to such a degree that other wizards may just start building towers and launch another round of the Mage Wars...
Ipslore the Red is one of the exceptions : he fled the halls of the Unseen University, married and had a family. The inevitable eighth son, Coin, is only a baby when Death arrives for Ipslore and the ex-wizard decides to choose his son's destiny. The future he picks for Coin includes wearing the Archchancellor's Hat of the Unseen University and, in an attempt to cheat Death, Ipslore enters his staff when he leaves his body. His intention is to guide Coin to his destiny....
Coin is roughly ten years old when he makes it to the University, and isn't long in taking over. When he deals with two of the Wizards - including the incoming Archchancellor - in a swift and very final manner, the remaining members of staff are understandably reluctant to stand against him. However, two of the survivors - a rather devious pair called Spelter and Carding - smell an opportunity. In seeing themselves as Coin's most senior and trusted advisors, they don't realise that Ipslore already has that role to himself.
Coin's arrival isn't universally welcomed - the rats and the gargoyles are amongst the first to flee, while the books in the University's library are distinctly unsettled. Rincewind, now acting as the University's honourary assistant librarian, is the first member of staff to realise there's something strange happening and nips off to the pub in a panic with the Librarian (an orang-utan), and his Luggage. (Luggage is a large brass-bound box, made from sapient pearwood - the same material wizard's staff is traditionally made from. It can move around by itself, has rather a vicious temper and - like Dr Who's Tardis - appears to be much bigger on the inside than on the outside). While Rincewind has been lucky enough to avoid Coin at the University, he's unfortunate enough to be apprehended by Conina at the Mended Drum. Conina, a very successful thief, is the daughter of Cohen the Barbarian and has pilfered the Archchancellor's Hat from the University. In this case, however, she stole the hat at its own request. (It is a magic hat after all...and it has realised that Coin's arrival will signal the Apocralypse). Under the Hat's instructions, Rincewind and Conina travel to Klatch, where the Hat believes there is a mind devious enough to wear it...and stand against the Sourcerer.
As usual from Pratchett, this is an easily read, rather silly and very enjoyable book.