This was the final Discworld book I hadn’t read (and intended to; I don’t plan to read Raising Steam or The Shepherd’s Crown). It’s far from the best of Discworld; I’d put it in the bottom third, for me, down with most of the Rincewind books. But it’s still definitely a Discworld book, with all the wit and associated warm fuzzies I could hope for.
Maurice the cat and his accompanying clan of rats learned to talk, like Gaspode, because the wizards at Unseen University are really bad at cleaning up their garbage. Since they learned to speak, Maurice has led the rats and a Stupid Looking Kid with a flute from town to town. The towns will suddenly get a plague of rats, and suddenly a rat piper will appear with his flute and lead the rats out of town - for a modest fee. The rats and the kid are both dubious of the morality of this enterprise, but Maurice assures them it’s all fine. Their doubts eventually take over, and they agree that the town they’re currently approaching will be the last. But then they find that there is something strange going on with this town, which already has a plague of rats…
This might well the bloodiest of all Discworld books, which was somewhat startling to me given that it’s also one of the explicitly YA ones. It’s enough that I want to give a content warning for animal cruelty (not just the traps and poisons the rats expect).
I put it in the lower end of Discworld for two reasons. One is that it dragged a fair bit; I think it would have been better if it was like 25% shorter. Nearly all of the denouement could have been cut, in my opinion. And the character of Malicia didn’t really work, in my opinion. She’s a character who thinks in terms of stories, which is an idea Sir Terry did immeasurably better with Granny Weatherwax.
But “not great Discworld” is still Discworld.