The Amazing Maurice and His Educated Rodents (Discworld #28)
Maurice, a streetwise tomcat, has the perfect money making scam. Everyone knows the stories about rats and pipers, and Maurice has a stupid-looking kid with a pipe, and his very own plague of rats-strangely educated rats...
But in Bad Blintz, the little con suddenly goes down the drain. For someone there is playing a different tune and now the rats must learn a new word.
E V I L
Its not a game any more. Its a rat-eat-rat world. And that might only be the start....