"The City of Ember" is a book about an underground city, Ember, that was created by "the Builders" to withstand an impending apocalypse. Ember was meant to provide enough supplies to survive for 200 years, and the story takes place 241 years after establishment. The mayor of Ember traditionally passed along a locked box to the subsequent mayor, with the box containing instructions on how to return to living above ground; however, the seventh mayor died, and the box disappeared.
"The City of Ember" is a science fiction novel by Jeanne DuPrau that takes place in a post-apocalyptic future. The city was built by doctors, engineers and scientists, referred to as "the Builders," to last 200 years. The first mayor was given a locked box with instructions for the city's inhabitants, and the box was to be passed down to each subsequent mayor. This transition perseveres until the seventh mayor, who (along with many citizens) contracts a deadly cough. He tries to open the locked box, in hope of a cure for the disease, but fails and dies before he can pass along the box or inform others of the importance.
Protagonist Lina finds the instructions left by the Builders 241 years after the city was constructed, deciphers the guidance and, along with her sister, Poppy, and friend, Doon, makes the steep climb to escape Ember. Nina, Poppy and Doon see for the first time that Ember is underground, and Nina throws a rock down to the city with instructions attached, hoping the citizens will see her note and escape.