The amazing Maurice and his Educated Rodents. Corgi Audio Books 2001 ISBN 0-552-14924-1

Maurice, a scruffy tomcat with an eye for the main chance, has the perfect fiddle going. He has a stupid-looking kid for a piper, and he has his very own plague of rats- rats who are strangely educated, so Maurice can no longer think of them as lunch. And everyone knows the stories about rats and pipers- and is giving him lots of money. Until they try the trick in the far-flung town of Bad Blintz, and the nice little con suddenly goes down the drain.
Someone there is playing a different tune. A dark, shadowy tune. Something very, very bad is waiting in the cellars. The rats must learn a new word.

Evil.

It’s not a game any more…