The Amazing Maurice and his Educated Rodents: Terry Pratchett

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.
EVIL.
It`s not a game any more. It`s a rat-eat-rat world. And that might only be the start . . .