Dreaming Spies is a book by Laurie R. King and was published in 2015. It is the thirteenth book in the Mary Russell and Sherlock Holmes mystery series.
The story starts in early 1924, in between the events of The Game and Locked Rooms. The caper starts innocently enough while on board a ship heading from India to California via Japan. But Russell and Holmes eventually find themselves involved with a British blackmailer, a group of Ninjas, and the Japanese crown prince Hirohito, finally resolved at Russell's stomping grounds of Oxford.