1895 London is scared. A killer haunts the city's streets; the poor are hungry; crime bosses are taking control; the police force is stretched to the breaking point. The rich turn to Sherlock Holmes, but the celebrated private detective rarely visits the densely populated streets of South London, where the crimes are sleazier and the people are poorer. In the dark corner of Southwark, victims turn to a man who despises Holmes, his wealthy clientele and his showy forensic approach to crime: Arrowood-self-taught psychologist, occasional drunkard and private investigator. When a man mysteriously disappears and Arrowood's best lead is viciously stabbed before his eyes, he and his sidekick Barnett face their toughest quest yet: to capture the head of the most notorious gang in London....