It doesn't seem quite right for this book to be touted as the prequel to City of Ember. Though a single character from this book does play a bit part in the story of Ember, the ties to the Ember story are hastily explained in the last 4 pages of Yonwood. It's almost as if a totally unrelated story was already written and then edited later to loosely fit into the Ember storyline. Honestly, it makes one feel kinda ripped off. What this book is really about is what can happen when someone thinks they are correctly interpreting God's will, and seems to preach that since everyone claims that their God supports their view, and these views are in opposition, no one should listen to anyone's claims of what God's will is, and we should just all follow our hearts. Which seems like a good idea until you realize that there's just as much opposition between what's in different people's hearts. It sort of comes off as a cautionary tale, and it's hard to tell if DuPrau is cautioning against religion as a whole or just bumbling but well-meaning interpreters of God's will. She may as well have used words like "Iraq" and "President Bush" and "WMDs" -- the allegory is that obvious. This book did keep me engaged, and it is a decent story. It's just very pretty misrepresentative to connect it to the Ember story. Marketing FTW, huh?