Nan Sparrow is one of London's countless "climbers" - children who spend their days cleaning chimneys. The work is brutal and dangerous. Thanks to her wits and will, Nan has managed to beat the deadly odds time and time again. But when she gets stuck in a chimney fire, it seems the end has come. Instead, she awakens to find herself unharmed in an abandoned attic. And she is not alone. Huddled in the corner is a mysterious creature - a golem - made from soot and ash.