In the year 241, twelve-year-old Lina trades jobs on Assignment Day to be a Messenger to run to new places in her decaying but beloved city, perhaps even to glimpse Unknown Regions.
While visiting the small town of Yonwood, North Carolina, eleven-year-old Nickie makes some decisions about how to identify both good and evil when she witnesses the townspeople's reactions to the apocalyptic visions of one of their neighbors.
In these first three books of Ember, young people in a future world face the fear of impending war, seek escape from a decaying underground city, and work to help immigrants make a home in a city stretched to its limits in the wake of "the Disaster."
When a roamer trades them an ancient book with only a few pages remaining, Lina and Doon return to Ember to seek the machine the book seems to describe in hopes that it will get their new community, Sparks, through the winter.