In spring 1914, the British intelligence receives information about a planned assassination of the Austro-Hungarian heir to the throne, Archduke Franz Ferdinand, which is said to be orchestrated by the Serbian secret organization known as the Black Hand. To avoid potential international complications and the threat of an impending war, the Prime Minister decides on a desperate measure: the famous detective Sherlock Holmes and his assistant Dr. Watson are forcibly recruited. Their mission is to stop the conspirators at all costs. Holmes and Dr. Watson know that they are hardly suited for this task. They have no language skills and are unfamiliar with the conditions in the Balkans. Soon, they begin to suspect that they have actually been assigned a very different role: they are merely to serve as decoys to mislead the conspirators.