The legacy of deeds

It is 1894, and Sherlock Holmes is called to a Covent Garden art gallery where dozens of patrons lie dead before a painting of the Undying Man. Holmes and Watson are soon on the trail of a mysterious figure in black, whose astounding speed and agility make capture impossible. The same suspect is then implicated in another murder, when the servant of a visiting Russian grand duke is found terribly mutilated in a notorious slum. But what links the two crimes, and do they have anything to do with the suicide of an unpopular schoolteacher at a remote boarding school?