Lina Mayfleet desperately wants to be a messenger. Messengers spend their days outside, running from one corner of the city to the other. Instead, she draws the dreaded job of Pipeworks laborer, which means she'll be stuck in tunnels.

Doon Harrow draws messenger - and asks to trade with Lina! 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 starting to flicker...

When Lina finds fragments of an ancient parchment, she and Doon put the pieces together to discover a message that seems to be directions out of the city. Is there something beyond the endless darkness? It will take all of Lina and Doon't bravery and ingenuity to find out.