Sherlock holmes and the mystery of Haut-Koenigsbourg

1909. Everyone fears that war is on the horizon and European authorities can't help but wonder why the German Kaiser decided to rebuild the castle of Haut-Koenigsbourg. To make matters even more suspicious, he has taken to organizing secret meetings at the castle since its inauguration. Following his victory over Moriarty, Sherlock Holmes had moved away from the crime scene, but this case will bring the famous detective back from his early retirement in Sussex.
What is really going on between the Emperor, the architect, the hatter, the Pope's legate, and the attractive historian ? In this diplomatic and military game of chess, it's hard to tell who is a friend and who is a spy. Elementary ? Don't speak too soon, my dear Watson...