After a lengthy case in India, Mary Russell and Sherlock Holmes are on the steamer Thomas Carlyle, bound for Japan. Though they're not the vacationing types, Russell is looking forward to a change of focus--not to mention the chance of traveling to a place Holmes has not visited before. The idea of the pair being on equal footing is enticing to a woman who often must race to catch up with her older, highly skilled husband. Aboard the ship, intrigue stirs almost immediately. Holmes recognizes the famous clubman the Earl of Darley, whom he suspects of being an occasional blackmailer: not an unlikely career choice for a man richer in social connections than in pounds sterling. And then there's the lithe young Japanese woman who befriends Russell and quotes haiku. Haruki Sato agrees to tutor the couple in Japanese language and customs, but Russell can't shake the feeling that the young woman is not who she claims to be. Once in Japan, Russell's suspicions are confirmed in a most surprising way. From the Imperial Palace in Tokyo to Oxford's venerable Bodleian Library, Russell and Holmes race to solve a mystery involving a small book with enormous implications of international extortion, espionage, and shocking secrets that, if revealed, could spark revolution--and topple an empire.