The book directly follows the events of The Colo(u)r of Magic, in which the reader left the wizard Rincewind hanging off the edge of Discworld, which is carried on the back of four elephants, which in turn are carried on the back of the giant tortoise Great A'Tuin. Rincewind's great skill is not at wizardry but at staying alive. He meets back up with Twoflower the Tourist and The Luggage, which is still eating some people and staring down others.
This time, Rincewind's goal (instead of just merely staying alive) is to save the Discworld from the end of time. Unless all eight spells (one of which resides in Rincewind's head) are read from the great book the Octavo, the Discworld will be no more. The problem? The spell in Rincewind's head. The spell does not wish to be read, yet one wizard back at Unseen University wishes to get his hands on Rincewind.
Rincewind encounters even more interesting characters in this book, notably Cohen the Barbarian and Bethan, the virginal sacrifice. The reader also gets a glimpse into the Realm of Death, which is surprisingly full of flowers and a quaint cottage. There is also a bit of time spent in a magical store, which can never be found in the same storefront twice.
Another whimsical book that I couldn't put down. Pratchett's book is smart and humorous, and finding the rest of his books will be great fun!