Having left the Metropolitan Police under a cloud, Whicher's days as a detective are behind him. However, when he saves a respectable country lady from a violent robbery in a dangerous part of London, she hires him to investigate the savage murder of her 16-year-old niece. The investigation pits Whicher against wealthy and powerful figures, as well his former colleagues in the Met, and leads to a psychiatric institution where he must confront his own demons.