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.
Lina and Doon are thrilled to see their people join them above ground in the vibrant village of Sparks, but suspicion and prejudice soon turn the villagers and newcomers against each other.
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.
