In what may very well be their final case, Sherlock Holmes, Dr. Watson, and Mycroft Holmes found themselves at the mercy of a supervillain named Eurus, one with a shocking amount of influence on all the events in the entirety of the series since 2010. Whether or not this chilling deus ex machina will be satisfying to fans remains to be seen, but the episode did deliver on the show’s usual predilection for references to the original texts of Sir Arthur Conan Doyle.

The title of this episode is “The Final Problem,” which is itself, a reference to the 1893 Doyle story of the same name in which Sherlock Holmes famously “died.” At the time, Doyle intended it as the last adventure of the character, ever. So, if this new version of “The Final Problem” is indeed the final episode of Sherlock of all time, then this is perhaps also the last bow for writers Mark Gatiss and Steven Moffat in their roles as bonafide Sherlock Holmes superfans. Here are 12 references and Easter Eggs they slipped into the Sherlock season 4 finale, “The Final Problem.”

Major spoilers for the Sherlock season 4 finale ahead.

Mr. Steed, I Presume?

LEFT: Mycroft's sword. RIGHT: The original Avengers.
LEFT: Mycroft's sword. RIGHT: The original Avengers.

When Mycroft believes he is under attack in his own home, he pulls a hidden sword out of his umbrella. This is a direct reference to the classic 1960s-1970s British spy show, The Avengers. In that show agent John Steed had a sword concealed inside of his cane or umbrella, although he very rarely actually used it. (The Avengers should not be confused with the Marvel team of the same name.) John Steed was played by Patrick Macnee for the majority of the show’s run. His most famous partner was Mrs. Emma Peele, played by Dame Diana Rigg.

LEFT: Oscar Wilde. CENTER: A Sherrinford the Prison. RIGHT: Sherlock does an Irish accent.
LEFT: Oscar Wilde. CENTER: A Sherrinford the Prison. RIGHT: Sherlock does an Irish accent.

Oscar Wilde Influenced Sir Arthur Conan Doyle

Mycroft and John both quote from Oscar Wilde’s The Importance of Being Earnest saying, “The truth is rarely pure and never simple.” While the Wilde reference is made clear, the secret easter egg might be a nod to Oscar Wilde having met Arthur Conan Doyle shortly before the author wrote his second Sherlock Holmes novel The Sign of the Four. Doyle met Wilde at a dinner with Joseph Marshall Stoddart the editor of Lippincott’s in 1888. Some claim Wilde even influenced Doyle to make Sherlock Holmes more “bohemian.”

Sherrinford Isn’t a Person

The much discussed apocryphal third Sherlock Holmes brother was believed by many Sherlockians to be “Sherrinford Holmes,” the eldest secret brother of Sherlock and Mycroft. The name “Sherrinford” is derived from Doyle’s original concept for Sherlock’s name. But now, in the universe of Sherlock, the word “Sherrinford” isn’t the name of the secret sibling, but instead a super-secret prison where Mycroft and Sherlock’s sister, Eurus, is locked up.

Holmes’s Irish Disguise

When Mycroft, Sherlock and John sneak into the Sherrinford Prison, Sherlock briefly affects an Irish-sounding accent. This is a reference to one of Sherlock’s aliases from the Conan Doyle stories. In the short story “His Last Bow” — found in the book of the same name — Sherlock Holmes uses the Irish-American alias of “Altamont” on a spy mission.

LEFT: The coffin from "The Disappearance of Lady Frances Carfax." RIGHT: "The Musgrave Ritual."
LEFT: The coffin from "The Disappearance of Lady Frances Carfax." RIGHT: "The Musgrave Ritual."

A Coffin That Doesn’t Fit

One of Eurus’s puzzles for John, Mycroft, and Sherlock involves analyzing a coffin to deduce who the coffin might be intended for. This recalls the Doyle story “The Disappearance of Lady Frances Carfax,” in which a trick coffin is central to the mystery’s solution. “The Disappearance of Lady Frances Carfax” can be found in the book His Last Bow.

“The Musgrave Ritual”

Just as with the two previous installments in this season, “The Final Problem” loosely adapts an original Sir Arthur Conan Doyle story. And though it carries the title “The Final Problem,” the episode actually uses “The Musgrave Ritual” for its basic structure. In the episode Eurus Holmes concocts a bizarre song which she claims contains clues, saying, “The song is the answer.” In the original story, a family’s strange riddle is revealed to be a treasure map hidden in plain sight. The final sequences in which Sherlock discovers the hiding place of Eurus directly references “The Musgrave Ritual.” The episode also takes great pains to remind us that this is one of Sherlock’s first cases, which is also a reference to the original story. “The Musgrave Ritual” is one of the rare stories in which Watson wasn’t working with Holmes at the time the adventure actually transpired. “The Musgrave Ritual” can be found in the book The Memoirs of Sherlock Holmes.

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LEFT: "The Gloria Scott" CENTER: John's shock blanket. RIGTH: The dancing men.
LEFT: "The Gloria Scott" CENTER: John's shock blanket. RIGTH: The dancing men.

Sherlock’s first Case in Sherlock and “The Gloria Scott”

When all is revealed in “The Final Problem,” Sherlock recalls his very first case, referenced back in the third episode of the first season; “The Great Game” when Sherlock was trying to figure out the murder of Carl Powers. This time, another murder of a young man is revealed: Eurus’s drowning of Sherlock’s childhood friend, Victor Trevor. This references the short story “The Gloria Scott,” in which one of Sherlock’s friends from college, Victor Trevor, accidentally recruited the young detective into solving a mystery for his father. Most fans consider and scholars consider Victor Trevor and “The Gloria Scott,” to be the definitive first case of Sherlock Holmes, chronologically speaking. Like “The Musgrave Ritual,” “The Gloria Scott” can be found in The Memoirs of Sherlock Holmes.

Shock Blanket

At the end of the episode, John is wearing a blanket. This is a reference to the first episode of Sherlock in 2010: “A Study in Pink.” In the final scenes of that episode Sherlock says, “Look at me, I’m in shock. I’ve got a blanket.” Fans around Twitter also often post pictures of themselves wearing shock blankets prior to new episodes of Sherlock airing.

“The Adventure of the Dancing Men”

In the final montage of the episode, several future cases of John and Sherlock are briefly glimpsed. One depicts a chalkboard adorned with stick-figures dancing. This references the story “The Adventure of the Dancing Men,” in which identical stick-figures are drawn in various parts of London as a kind of secret message. This story was also loosely adapted in the first season episode “The Blind Banker.” The story “The Dancing Men” can be found in the book The Return of Sherlock Holmes.

Various Reichenbachs and a Supervillain Out of Nowhere in “The Final Problem”

LEFT: Reichenbach Falls in Sherlock's mind. RIGHT: Sidney Paget's illustration for "The Final Problem."
LEFT: Reichenbach Falls in Sherlock's mind. RIGHT: Sidney Paget's illustration for "The Final Problem."

In an attempt to truly adapt the original short story, “The Final Problem,” it is revealed that Sherlock’s subconscious is preoccupied with “water” because of the emotional trauma Sherlock experienced after the drowning of Victor Trevor. In “The Great Game,” Moriarty and Sherlock met at a swimming pool, while the dream sequences in “The Abominable Bride” created a the actual Reichenbach Falls from the short story version of “The Final Problem.” Plus, the existence of Eurus could be seen as its own reference to the Doyle version of “The Final Problem.” At the time which it was published in 1893, Moriarty had never appeared in any other Sherlock Holmes stories, and yet in an effort wrap things up, Arthur Conan Doyle*retroactively attributed tons of past ills to Moriarty’s grand criminal influence.

This latest (and possibly last) episode of Sherlock does something similar: retroactively attribute nearly everything that’s happened in the entire show to the actions of one character who we’ve never met before. So, in a sense, an evil deus ex machina is actually a classic Holmes tradition.

Finally, when Mary Watson says “the best and wisest men I’ve ever known,” this is a paraphrase of Dr. Watson’s last line in “The Final Problem” when he believes Sherlock Holmes has died: “The best and wisest man whom I have ever known.” The story “The Final Problem” is the last story in the book The Memoirs of Sherlock Holmes, though sometimes both The Adventures and Memoirs are collected into one volume.

Rathbone Place

The final shot of “The Final Problem” has John and Sherlock running at the audience heroically. This recalls the promotional shots for the first season of the show. But behind them is an even more classic nod. The building they are running from has a plaque that reads “Rathbone Place.” Basil Rathbone is arguably the most famous actor have ever played Sherlock Holmes, starring in the role over fourteen times from 1938 through 1946.

Ryan Britt is an Associate Editor at Inverse where he specializes in science fiction. He is the author of the 2015 essay collection Luke Skywalker Can't Read and Other Geeky Truths from Plume/Penguin Random House. Ryan's other writing has been published in the New York Times, Tor.com, VICE, Den of Geek! and elsewhere. He lives in New York City with his family.