The City of Ember by Jeanne DuPrau
This book is about a girl named Lina Mayfleet who wants to be a messenger, but is forced to be a Pipeworks laborer. It is also about a boy named Doon Harrow, who draws messenger, but wants to trade with Lina! Doon wants to work underground because the generator is breaking, and he wants to try and fix it. These children live in an underground city called Ember, that is in severe danger, and they discover it is up to them to save it! I thought it was a pretty good book. The ending is disappointing, though. I do recommend this book to others.