Unscrupulous boxing promoters, violent bookmakers, a Russian gangster, incompetent amateur robbers and supposedly Jewish jewelers fight to track down a priceless stolen diamond.
Dr Trevelyan calls on Holmes on behalf of his friend Blessington, after a Russian father and son vanish during a consultation. Blessington knows of no one who wishes him ill, but he is found hanged the next day. Holmes investigates, with advice from Watson.