Dr. Poppy Stamford, sister of the man who would introduce John Watson to Sherlock Holmes, teams up once again with Sherlock in a new adventure. One of Sherlock's Baker Street Irregulars, Wiggins, uncovers a dismembered body in a shallow grave. Poppy and Sherlock set out to solve the murder and suddenly discover that it may be linked to the mysterious mutilation of Her Majesty's swans. Working under the eerie cloak of one of the most devastating fogs in London's history, the case takes Poppy and Sherlock from the most sordid neighborhoods of dirty, old Victorian London to the lofty halls of the Privy Council.