Sourcery is the first of the Rincewind subseries of Discworld not to also feature Twoflower. It makes sense–his story seems to have been told–but it still does feel a bit different.
Instead, we deal with the 8th son of a wizard (already the 8th son of an 8th son themselves)–a Sourcerer. Basically, one who can intuitively do magic on a scale wizards literally cannot dream of. They’re the entire reason that wizards are banned from having sex (see the 8th son bit above). And now there’s a new one in the world–a ten year old boy.
There is a bit more than that, involving accidentally preventing an apocalypse by way of stealing three of the four Horsemen’s horses, a book taught barbarian, more fun with the librarian turned orangutan (but still the librarian), and other assorted hijinks.
Overall, the novel is a lot of fun. I like the parts with either Rincewind or the Sourcerer more than the B-plot, although there’s a lot of fun even there. It continues to contain a wonderful mix of humor along with world ending chaos and terror from other dimensions in a way few other authors have managed.
It’s an enjoyable novel and I can already see how Pratchett continued to sharpen his craft with each successive novel. I look forward to seeing how the Rincewind series progresses as it jumps through the main series (it contains Discworld novels 1, 2, 5, 9, 17, 22, and 37, so pretty much the entire range).