I finally tracked down this prequel to The Gammage Cup, and it was worth the hunt. The Firelings have lived for generations on the slopes of Belcher, an active volcano. They survive by following strict rules on how to live and where not to go, along with an occasional human sacrifice down the Long Slip when Belcher gets hungry. But Belcher gets really sick, doom hangs over the Firelings, and their only chance of survival is in breaking all the rules.

It is full of memorable characters and plenty of action. It is also an exploration of the danger of unquestioning belief and conformity. ( )

A sort of prequel to the Minnipins stories in which there are little people living on a set of stony islands shaped like a man, which they believe was a heavenly being who fell to earth. One has a volcano they regard as the god's belly, and when it rumbles they think someone should be sent down a slide into it as a sacrifice. There are a set of story stones which act as the holy scriptures of this religion. No one has been sacrificed for a long time, but now the "belly" of Belcher is rumbling again and thy think it may be time...

One of my favorites.