Russell heads for Oxford to resume her long-delayed studies when she comes face-to-face with a young Japanese woman who is not all that she seems.

Mary Russell and her husband, Sherlock Holmes, are swept up in a baffling case that will lead them from the idyllic panoramas of Japan to the depths of Oxford's most revered institution. Aboard the steamer Thomas Carlyle, Holmes recognizes the Earl of Darley, whom he suspects of being an occasional blackmailer. And then there's the lithe, surprisingly fluent young Japanese woman who befriends Russell and quotes haiku. She agrees to tutor the couple in Japanese language and customs, but Russell can't shake the feeling that Haruki Sato is not who she claims to be.