"William James Moriarty and Sherlock Holmes meet again on a train back to London, and a dead body is discovered in a locked passenger cabin. With John Watson named as the prime suspect, Sherlock challenges Moriarty to a contest of who can solve the murder first. Will Sherlock be able to clear Watson's name? Back in London, a state secret that only the royal family is privy to has been stolen and MI6 is tasked with retrieving it, lest the whole empire fall into ruin"-- Provided by publisher.