The Amazing Maurice and His Educated Rodents (Discworld, #28)

The Amazing Maurice and His Educated Rodents (Discworld, #28) - Terry Pratchett Some rats eat some rubbish from the Wizards and gain sentience, along with a cat who then use a boy to pull a pied piper stunt, they've been chased from a few towns and now they're in Bad Blintz but there's something wrong here something evil and it will take Cat, Rats and boy to fix it.