The City of Ember
by Jeanne DuPrau
Ember is the only light in a dark world. But when its lamps begin to flicker, two friends must race to escape the dark.
The city of Ember was built as a last refuge for the human race. Two hundred years later, the great lamps that light the city are beginning to dim. When Lina finds part of an ancient message, she's sure it holds a secret that will save the city. Now, she and her friend Doon must race to figure out the clues to keep the lights on. If they succeed, they will have to convince everyone to follow them into danger. But if they fail? The lights will burn out and the darkness will close in forever.