Days after the encounter between Holmes and Moriarty at the Reichenbach Falls, Pinkerton detective agent Frederick Chase arrives in Europe from New York. Moriarty's death has left a poisonous vacuum in the criminal underworld, and there is no shortage of candidates to take his place, including one particularly fiendish criminal mastermind. Chase and Scotland Yard Inspector Athelney Jones, a devoted student of Holmes' methods, must forge a path through the darkest corners of England's capital, from the elegant squares of Mayfair to the shadowy wharfs and alleyways of the London Docks, in pursuit of this sinister figure.