1914. Sherlock Holmes has been murdered. Nobody knows who did it, but Wiggins, former Baker Street Irregular and Holmes' protégée, suspects a German spy. However, Europe is descending into the chaos of the First World War. Captain Kell of Military Intelligence has limited resources, and more pressing matters on his mind. Wiggins is on his own. Almost. He pursues Holmes' killer across the continent, but as grief and rage close in it's not just the killer that eludes his grasp...