The famous London detective Sherlock Holmes is talking with his friend and companion John Watson when he receives a visit from a masked man, whom he deduces is actually Wilhelm Gottsreich Sigismond von Ormstein, the king of Bohemia. Once the man is unmasked, he asks for Holmes’s help retrieving a very valuable set of photographs. The King is engaged to a Scandinavian princess, but is worried that the princess’s family would disapprove of his previous relationship with a young American opera singer named Irene Adler. Ms. Adler has evidence of this relationship, namely photographs of the two of them together, and has refused to return them to the King. His agents have offered to buy them from her and have even broken into her home in an attempt to steal them, but neither tactic was successful. Holmes is the King’s last hope of retrieving the photos. Holmes agrees, and invites Watson to join him.
Dressed as an out of work groom, Sherlock goes to Irene Adler’s house and gathers valuable information from her workers: she has a gentleman caller, a lawyer named Godfrey Norton, who can be expected at the house at least once per day. Mr. Norton soon arrives at Ms. Adler’s house and then they both leave for St. Monica’s Church, followed by Holmes, still disguised as a groom. He is swept into the church to witness the marriage of Ms. Adler and Mr. Norton, and then observes them go their separate ways after the ceremony.
Holmes returns to Irene’s house that evening, this time dressed as a clergyman. He stages a fight with some men on the street and Irene brings him in to tend to his injuries. Once inside, he signals to Watson, who throws a small rocket into the house and yells “Fire!” Irene runs to a panel in her sitting room to protect the photographs of her and the King. Holmes observes this, and know knows where the photographs are hidden; he informs her that the fire was a false alarm, and he later leaves and meets up with Watson on the street. As the two men walk back to 221B Baker Street, they discuss plans to retrieve the photographs early the next morning. When the get to the front door, a young person walks by and says “Good-night Mister Sherlock Holmes,” in a voice that is familiar to Holmes, though he cannot place it.
Upon arriving at Irene Adler’s home the next morning, the men find that she has already left England, but has addressed a letter to Sherlock. She congratulates him for tricking her into letting him in her home, but notes that she quickly saw through the clergyman disguise. She also reveals that it was she, dressed as a young man, who greeted him the night before at the door of 221B Baker Street. She and her new husband, Mr. Norton, have left England permanently, taking the photographs with them; the King need not worry, however, because she loves her new husband and has no desire to impede the King’s royal wedding.
The King is satisfied with this outcome to the case, and offers Sherlock an emerald snake ring as payment. Sherlock refuses the ring and instead requests a photo of Irene—one that she left behind with the letter—as a memento of the most remarkable woman he has ever met.
