In this episode, the modernised Sherlock catchphrase "The Game is on!" is rendered back to the original "The Game is afoot."
The case of "Ricoletti of the club foot and his abominable wife" is an unrecorded case from the official Holmes canon. Sir Arthur Conan Doyle mentioned it in the short story "The Musgrave Ritual," but never wrote a full story about it.
Like in the original stories, Holmes and Watson address each other by their last names, as such was more common in Victorian times. Also, the Victorian version of Watson addresses Moriarty as "Professor" for the first time in the entire show.
Despite several jokes about Mycroft's weight throughout the series, this is the first episode where Mycroft is presented as grossly overweight as described in Doyle's original story, "The Adventures of the Greek Interpreter" (1894).
When John and Mary are arguing at 221B Baker Street, Sherlock is playing the violin composition he had written and performed for their wedding, as seen in Series 3, Episode 2: "The Sign of Three."