The City of Ember by Jeanne DuPrau
Many hundreds of years ago, the city of Ember was created by the Builders to contain everything needed for human survival. It worked - but now the storerooms are almost out of food, crops are blighted, corruption is spreading through the city and worst of all - the lights are failing. Soon Ember could be engulfed by darkness-But when two children, Lina and Doon, discover fragments of an ancient parchment, they begin to wonder if there could be a way out of Ember. Can they decipher the words from long ago and find a new future for everyone? Will the people of Ember listen to them?