The City Of Ember by Jeanne DuPrau

This book is about a girl named Lina, and a boy named Doon. They lived in an underground city called Ember. Before the city was made, the builders wanted to make the people to live in Ember for 240 years. The builders made a locked box with an instruction to get out in 240 years. The mayors of Ember would pass the box secretly to their children year after year, until the box opened. One day, a mayor died, just before the mayor could tell his son about the instruction, so the instuctions got lost; somewhere in Ember.
Doon was a pipeworker, and was very interested in mechanism. One day, Lina's younger sister, Poppy, found the box in a closet, and was chewing on the paper! Lina quickly took the paper away from Poppy. She and Doon were going to decode it and save Ember.
Five Stars
Joseph