Young chimney sweep Tom has started seeing strange, supernatural things – fairies in the flowers by the river, a soot monster crouching in the darkness of a chimney, and then the mysterious river spirit Elle. Elle joins Tom and the other children apprenticed to cruel master sweep Mister Crow. Together, they shimmy up the town's narrow, filthy chimneys. But Tom has an ominous feeling in his bones, and when he faces his most dangerous job of all, the reason for Elle's magical appearance becomes clear . . .