Trivia
Douglas Wilmer, seen in the Diogenes Club, played Sherlock Holmes in Sherlock Holmes and The Adventure of Sherlock Holmes' Smarter Brother.
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In the first sequence in which various newspaper headlines are shown, one story begins, "In a twist worthy of a Conan Doyle novella, Mr. Sherlock Holmes was yesterday revealed to be an expert witness at the trial of 'Jim' Moriarty."
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Moriarty keeps referencing his "Final Problem" - namely, how he and Sherlock will settle their score. This is a reference to the Sherlock Holmes story "The Final Problem," which was the basis for this episode.
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Katherine Parkinson, who played journalist Kitty Riley in this episode did a series of Malteasers adverts with Amanda Abbington, Martin Freeman's wife.
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When Sherlock and John escape from the police, on the wall in the background there is a graffiti that reads 'IOU', Moriarty's 'threat' to Sherlock.
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