What is the plot of the 'Discworld' books?

Discworld is a world on which the Discworld novels (numbering 39 come 13th October 2011) is set. It is (obviously) disc-shaped, and carried on the back of a giant turtle called Great A'Tuin that flies (or swims) through space. On the back of A'Tuin stand four elephants that support Discworld. The Disc is roughly 10,000 miles wide and at the centre is the 10 mile high rock spire/mountain Cori Celesti, home of the gods. Notable places include the famous (or infamous) city-state of Ankh-Morpork, the only place in any world where you can walk on the river. There is also Quirm (comparable to France), Ephebe (Greece), Klatch (Arabia), the Agaetean Empire (China) and Uberwald (Germany/Slavic countries). It is inhabited by humans, trolls, dwarfs, Igors, vampires, werewolves, golems, gnomes, the Nac Mac Feegle and many more. I hope this encourages people who haven't read Discworld to read one today. THEY ARE THE BEST BOOKS IN THE WORLD!