The City of Ember — Jeanne Duprau

Citizens of Ember shall be assigned work at twelve years of age...

LINA MAYFLEET desperately wants to be a messenger. Instead, she draws the dreaded job of Pipeworks laborer, which means she'll be working in damp tunnels deep underground.

DOON HARROW draws messenger--and asks Lina to trade! Doon wants to be underground. That's where the generator is, and Doon has ideas about how to fix it. For as long as anyone can remember, the great lights of Ember have kept the endless darkness at bay. But now the lights are beginning to flicker. .. .