The year is 1895. It is the third week in September and a dense yellow fog has settled over London. Holmes is frustrated at the complete lack of criminal activity when he gets a letter from his brother, Mycroft. The letter is about a young man called Cadogon West who was killed mysteriously on the London Underground. The plot thickens when it turns out young West worked for the British Government on top secret work. Only Holmes can get to the bottom of this mission of national importance - the peace of Europe depends on it.