Frieda Klein is a solitary, incisive psychotherapist who spends her sleepless nights walking along the ancient rivers that have been forced underground in modern London. She believes that the world is a messy, uncontrollable place, but what we can control is what is inside our heads. The abduction of five-year-old Matthew Farraday provokes a national outcry and a desperate police hunt. And when his face is splashed over the newspapers, Frieda cannot ignore the coincidence: one of her patients has been having dreams in which he has a hunger for a child. A red-haired child he can describe in perfect detail, a child the spitting image of Matthew. She finds herself in the center of the investigation, serving as the reluctant sidekick of the chief inspector.