Clod is an Iremonger. He lives in the Heaps, a vast sea of lost and discarded items collected from all over London. At the centre is Heap House, a puzzle of houses, castles, homes and mysteries reclaimed from the city and built into a living maze of staircases and scurrying rats. A storm is brewing over Heap House. When Clod meets Lucy Pennant, a girl newly arrived from the city, everything changes. The secrets that bind Heap House together begin to unravel to reveal a dark truth that threatens to destroy Clod's world.