Stripfettle's Believe It Or Not Grimoire
It has been noted that the Librarian has a happy knack for uniting a searcher after knowledge with exactly the right book they need at just the right time.
Such a book delivered in a timely manner to Windle Poons was Stripfettle's Believe-It-Or-Not Grimoire.
This contained the awful warning about the fate that befell the city of Kahn-Li, when a plague of little carts happened, which at first the population did not recognize as a plague because they were so incredibly useful. However, the carts had another purpose in mind, or rather in the mind of the entity directing them...
Kahn-Li, written as Khanli, is a country or region marked on The Discworld Mapp.