A masked man calls, on confidential business, and Holmes quickly recognizes the visitor as the King of Bohemia. The King is planning for himself a dynastic marriage and is worried about a compromising photograph in the possession of his American former mistress. He wants Holmes to get it back for him.In outwitting the lady, Irene Adler, Holmes goes to great lengths - and at the end of the affair Watson comes to the conclusion that his friend is himself smitten.

A plumber, John Horner, is arrested just before Christmas and charged with stealing a famous jewel, the Blue Carbuncle, from Lady Morcar. He denies the theft - but he has a criminal record, and all the evidence is against him. After Holmes's doorman finds the Carbuncle in a Christmas goose, Holmes uses an old hat to track the goose to a poultry dealer, then traps the servant who stole the jewel and framed the plumber. The Blue Carbuncle has a dark history, and the stone features in the programme's opening credits with turbulent scenes from its past.

The French government sends for Holmes when the Mona Lisa is stolen from the Louvre. Holmes swiftly decides he is dealing with a mastermind - and none other than his old enemy Professor Moriarty himself.Holmes foils Moriarty's plans to sell Leonardo da Vinci's masterpiece and trails him to Switzerland, where they meet and fight to the death above the famous waterfall at Reichenbach.