The Amazing Maurice and his Educated Rodents

The Amazing Maurice and his Educated Rodents is the 28th novel in Terry Pratchett's Discworld series, published in 2001. It was the first Discworld book to be aimed at the younger market, followed in that by The Wee Free Men in 2003.

Warning: Wikipedia contains spoilers

The Amazing Maurice and his Educated Rodents is a group of talking rats who go from town to town being a "pest" so that their accomplice, a boy piper, can "lure them all away" from the town, after which they share the money the piper makes.

All goes well until they arrive at a town in which the rats were such a big problem once that the town has started offering money for every rat tail people bring. Of course soon the town is controlled by two rat catchers who only pretend to be catching rats (they are now paid for the shoe laces they give to the major, but nobody gives the laces a close look as everyone knows rats cause horrible diseases) and so the rat catchers get all the town's money and food while the rest of the town is starving. It's up to Amazing Maurice and his Educated Rodents to break up their act and save the town.