On a cold November morning, a young American actress visits 221B Baker Street, desperate for Sherlock Holmes to protect her from the threats of a mysterious, menacing man who has recently appeared in her life. Holmes agrees to help, even though he has just promised the Prime Minister to solve the murder of John D. Rockefeller’s security agent before the incident can derail an upcoming British-American summit. To find the agent’s killer―and help the young actress―Holmes will need all his talents for both deduction and deception. But when another lovely woman, this one from Holmes’s past, reappears and clues to the murder point to the late Professor Moriarty, the famously analytical detective must also look inward. Can Holmes prevent chaos on both sides of the Atlantic and unmask his newest client’s shadowy antagonist? For Holmes and Watson, this is the case that will change everything.