A sister searches for her missing brother as a new power rises amid the splendour and the squalor of a once great city. Lower Rhumbsford is a city far removed from its glory days. On the banks of the great river Rhumb, its founding fathers channelled the river's mighty flow into a subterranean labyrinth of pipes, valves and sluices, a feat of hydraulic prowess that would come to power an empire. But a thousand years have passed since then, and something is wrong. The pipes are leaking, the valves stuck, the sluices silted. The erstwhile mighty Rhumb is sluggish and about to freeze over for the first time in memory. In a once fashionable quarter of the once great city, in the once grand ancestral home of a family once wealthy and well-known, live the last descendants of the city's most distinguished engineer, siblings Samuel and Briony Locke.