The action-packed mystery begins when the Crown Prince of Bohemia, who is to become the future Kaiser of the German Empire, hires Sherlock Holmes to retrieve acutely embarrassing photographs covertly taken of him with notorious opera diva Irene Adler in her boudoir. Holmes suspects that if Adler is involved, the case is much more complex – and certainly darker and deadlier. Holmes’s brother, Mycroft, is the British government’s Chief of Intelligence and he questions Holmes about the Crown Prince’s visit.  Now Holmes is certain that the scandalous photographs are not all that the Crown Prince is after. And he is right. The British have just developed a submarine and the Germans want the plans.