The wizards of Unseen University must once again defend Roundworld (aka Earth), not against elves or humans" ignorance, but against Discworld"s Omnian priests, who have issued a writ claiming ownership of it. The Omnians fervently believe that the world is round, not flat, and view the discovery of Roundworld as a vindication of their faith. They argue that to leave this artifact in the hands of the wizards would be unacceptable: not only do the academics claim that Discworld is a flat world traveling through space on the back of a turtle, but by creating the Roundworld universe, they have elevated themselves to the level of gods. Ankh-Morpork"s venerable tyrant Lord Vetinari agrees to a tribunal, where the wizards Ridcully, Rincewind and Ponder Stibbons can present their case, with key assistance from a Roundworld librarian named Marjorie Daw. Interwoven with the Discworld chapters are Pratchett, Cohen and Stewart"s explorations of such topics as big science, creation (dicussing...