When she returns home after two years, Fever finds that her Scriven mother's creation, New London, the city on wheels, is nearly complete and ready to fight the nomad tribes of Britain--and Fever must journey to the north to find the ancient birthplace of the Scriven mutants and solve the mystery of her own past.

Fifteen-year-old Mistletoe lives in the sub-canopy zone amid poverty and outdated technology, but when she meets Ambrose Truax, the privileged sixteen-year-old heir to the Unison empire and they discover they share a sinister link, they begin a frightening journey into the uncharted territory of the Unison 3.0 upgrade.