The City of Ember by Jeanne DuPrau

Ember was created 240 years ago as a completely isolated society. The city has no factories, no computers, no cars, or anything requiring electricity except for lights. Although the Builders provided canned goods and other necessary items for future citizens, the city is now running out of supplies and the lights are becoming more and more unreliable. People are starting to panic, because they don't know how to get help or if there is even a world beyond the city. Outside the city limits is complete darkness, and no one has a portable light source. Two kids discover a secret message that may unravel the mystery of the Builders and the outside world. Unfortunately the message was partially destroyed, and they will have to guess what the missing words are. This will lead them to an adventure that will take great courage but may save the citizens of Ember.

The story of Ember continues in The People of Sparks. Unshelved added The City of Ember to their Book Club comic strip.