The play begins with the announcement of the death of Sherlock Holmes. It is 1891 London; and Dr. Watson, Holmes’s trusty colleague and loyal friend, tells the story of the famous detective’s last adventure.
To begin the story, Holmes summons Watson to his home on Baker Street and tells him of the malevolent villain, Professor Moriarty, and how Holmes has, during the past six months, tried to piece together evidence that would convict him of his crimes. Holmes has determined that in order for Moriarty to be apprehended, he and his men must be apprehended all on the same day. The police will require a full week to organize the plan, and, for their personal safety, Holmes and Watson must leave town until the arrests have taken place. They are discussing this plan to leave London when an intruder bursts in, demanding to talk with Holmes.
Holmes deducts that the intruder is the King of Bohemia, who has come in desperation for the detective’s help. Before the King’s wedding in two week’s time, he must recover personal items, including a photograph, that connect him romantically to the famous opera star, Irene Adler. Adler is blackmailing the King and threatening his marriage. Holmes agrees to this one last case before returning his focus to the case of Moriarty.
The next morning Holmes and Watson set out to find Irene, whom the King says is in London. They follow a frantic couple to a church, where Holmes is dragged into being a witness for their hasty marriage. Fortunately, the woman turns out to be Irene. The man she just married is Mr. Godfrey Norton, and he quickly exits to ready the couple to leave the country. The secretive wedding intrigues Holmes, who also has feelings for this famous singer.
Holmes and Watson continue their search for the photograph, this time going to Briony Lodge where they find only a note from Irene to Holmes, which leads Holmes to deduce some vital facts about her situation. Unexpectedly, it becomes clear that there is a link between her, her new husband, and Holmes’s arch-nemesis, Moriarty. As if things weren’t complicated before, Holmes and Watson now find themselves entangled in a much deeper mystery. What revelations will be made and who will come through alive—or dead?