Autumn, 1897. As fog and unrest descend on London, a renowned Kensington spiritualist delivers an extraordinary message: the ghost of a murdered man has appealed to Sherlock Holmes for justice.Holmes dismisses the séance as nonsense-until a body bearing the dead man's distinctive scar is pulled from the Thames.. As London grows ever more unsettled, only the razor-sharp minds of Mrs Hudson and her resourceful assistant Flotsam can separate superstition from murder - and expose the killer before another victim is claimed.