Two teenagers dominate the story, one who longs to be a messenger because the job will allow her to venture above ground, while the other dreams of working underground to repair a generator whose failure will doom the city's power supply.
As my library aide used to say, "Fool, fool, fool..."
They are going to give away the mystery of Ember from the onset?
I know movies always change things but the why and where of Ember was the whole point of the story.
To quote Strother Martin as Percy Garris in Butch Cassidy and the Sundance Kid:
Percy Garris: Morons. I've got morons on my team.