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.
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.
