The Science of Discworld IV - Judgement Day

Marjorie Daw is a librarian, and takes her job - and indeed the truth of words - very seriously. She doesn't know it, but her world and ours - Roundworld - is in big trouble. On Discworld, a colossal row is brewing. The Wizards of Unseen University feel responsible for Roundworld (as one would for a pet gerbil).