Thousands of years after civilization was destroyed by a cataclysmic event, humankind has adapted and a new way of living has evolved. Gigantic moving cities now roam the Earth, ruthlessly preying upon smaller traction towns. Tom Natsworthy—who hails from a Lower Tier of the great traction city of London—finds himself fighting for his own survival after he encounters the dangerous fugitive Hester Shaw. Two opposites, whose paths should never have crossed, forge an unlikely alliance that is destined to change the course of the future.