The People of Sparks follows Jeanne Duprau's The City of Ember in plot and, sadly but expectedly in a sequel, in quality. Emberites have lived a sheltered life but even those of Sparks seem to know but little more of their common past. I realize Duprau wanted to explore tension and conflict resolution between the two communities and not their background, but I guess I am engaged enough in the story that I want to know more.
Actually, the theme of recovering post-apocalyptic community was done a little better than in Lois Lowry's recent Messenger. I do not understand how a world that contained the societies of Gathering Blue and Messenger could also contain that of The Giver, but it's the personalities Lowry wanted to combine in Messenger, not the societies. The macguffin could have worked if it had a source instead of being so starkly a deus ex machina.