The Iremongers are a mean and cruel family, robust and hardworking, living in the Heaps, a vast sea of lost and discarded items. A storm is brewing over Heap House. The Iremongers are growing restless and the whispers are getting louder. When Clod meets Lucy, 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.

In the aptly named borough of Foulsham, Grandfather Umbitt Iremonger has found a way of making everyday objects assume human shape, and turning real people into objects. Lucy Pennant has been discarded as a clay button, abandoned in the Heaps. Meanwhile, Clod has been turned into a gold coin and is being passed as currency through the town. Everywhere people are searching for Clod, who, it is believed, has the power to bring the mighty Umbitt down.

Foulsham has been destroyed. Darkness lies heavily over the city; the sun has not come up for days. Inside the houses throughout the capital, ordinary objects have begun to move. There are rumours of a terrible contagion. From the richest mansion to the poorest slum, people have disappeared. The police have been instructed to carry arms. Someone has stolen a certain plug. Someone is lighting a certain box of matches. All will come tumbling down. The Iremongers have come to London.