10-year-old Lee lives with her family and about a hundred thousand others in a dome that keeps them safe from all the dangers of the Outside. 
Usually, every day in the dome is pretty much exactly like all the others, but lately, Lee has been feeling restless and unsettled in a way she has never experienced before. Finding out that she is about to become a big sister adds to the disturbances of her usually strict routines, and one night, Lee sees something she was not supposed to.
A yearning for something different leads to Lee being forced to spend an entire day in the dangerous and toxic Outside. Can she survive all alone in the wilderness? And what would be worse, being all alone or discovering that she is in fact not alone at all?