The second episode of the new fourth season of Sherlock pushed the famous consulting detective of Baker Street and his long-suffering best friend, Dr. John Watson (Martin Freeman), into darker territories than perhaps ever before. But while Sherlock Holmes (Benedict Cumberbatch) matched wits with the scheming Culverton Smith (Toby Jones), his latest adventure, “The Lying Detective,” managed to slip in plenty of references and nods to Sir Arthur Conan Doyle’s original canon of nine books, consisting of 56 collected short stories and four novels. Like its predecessor, “The Six Thatchers,” “The Lying Detective” both adapted one specific Conan Doyle original while simultaneously referencing not only the whole Holmes universe, but a few other universes, too. There was even an obscure shout-out to a Doctor Who episode! Here are 12 easter eggs you might have missed in “The Lying Detective.”

Huge spoilers for “The Lying Detective” ahead.

Sherlock’s Drug Addiction and Wiggins

Early in the episode, it’s clear that Sherlock Holmes is hitting the needle pretty hard. This is a reference to Sherlock injecting cocaine in the original canon, notably in the novel The Sign of the Four, in which Sherlock Holmes mentions his own cocktail of narcotics as a “seven per-cent solution,” and even offers some to Watson after the doctor inquires if Holmes is doing morphine or cocaine. Holmes shooting-up cocaine is specifically mentioned again in the stories “The Five Orange Pips,” “The Man With the Twisted Lip,” and “The Yellow Face.” In “A Scandal in Bohemia,” Watson writes of Sherlock’s “drug-created dreams.” This notion is referenced later in the episode as Sherlock believes he has hallucinated Culverton Smith’s daughter, Faith.

Sherlock’s drug hook-up in this episode is named “Wiggins,” and he’s been seen on the series before. Wiggins (Tom Brook) first appeared in the third season finale “His Last Vow” and is based on the canonical character of Wiggins, a street urchin in Holmes’s employ in A Study in Scarlet. In the books, these urchins are called “The Baker Street Irregulars,” but in the show Sherlock, he just refers to them as his “homeless network.”

“The Problem of Thor Bridge”

When Sherlock walks the city streets with Faith Smith, it’s heavily implied that the character threw herself off of a bridge. This vaguely recalls the original Conan Doyle story “The Problem of Thor Bridge” in which a jealous lover does indeed commit suicide in order to frame another person for murder. The details in this episode are of course different (and Faith Smith’s “suicide” still murky) but the imagery of the bridge seems to be a direct reference to this latter-era short story, published in in 1922 and collected in the book The Case-Book of Sherlock Holmes.

“The Games Afoot!” and Shakespeare’s Henry V

In a rousing and excited moment for Benedict Cumberbatch, Sherlock recites nearly the entirety of a famous speech from Shakespeare’s Henry V which starts with “Once more unto the breach, dear friends!” Sherlock ends this rant with his famous catchphrase “the game’s afoot!” While this marks the first time Cumberbatch-Sherlock has uttered this phrase (usually saying “the game is on!”), this phrase was actually appropriated by Conan Doyle from Shakespeare in the first place because “the game’s afoot” was originally part of that Henry V speech. In a similar appropriation, Sherlock Holmes says, “There is nothing new under the sun” in A Study in Scarlet, which he kind of stole from the King James Bible.

Meanwhile, Sherlock Holmes first ripped off the “the game’s afoot!” from Shakespeare in the story “The Red-Headed League.” Weirdly, with its preoccupation with red hair, that story seems to be vaguely referenced by the fact that this episode reveals Watson’s “mistress” had a fake red wig.

Sherlock Shooting the Wall

In the same scene, Sherlock Holmes shoots up the walls of his Baker Street with manic glee. This is a reference to the story “The Musgrave Ritual” where Sherlock fires his revolver into the wall to create the initials “V.R.” which stands for “Victoria Regina,” the Queen of England during the Victorian age. In The New Annotated Sherlock Holmes, scholar Leslie Klinger referred to this as “Holmes the decorator.”

“The Dying Detective”

As with “The Six Thatchers,” nearly the entire plot of this new episode is structured loosely around a specific story, despite referencing many. In “The Dying Detective,” Sherlock Holmes pretends to be on his deathbed, the victim of a terrible poison, all in order to lure the evil Culverton Smith into a full confession at his bedside. Nearly everything in “The Lying Detective” plays out the same way as it did in the original story. Instead of feigning poison, Sherlock pretends to be high on drugs. Instead of Watson hiding behind the bed as he did in the story, this time, a recording device has been placed in Watson’s walking cane. Watson’s competence as a medial doctor is questioned in the original story, too. And, even Mrs. Hudson manically driving to see Watson and inform him of Sherlock’s poor health does in fact come from this story. Though, obviously in the original story she wasn’t driving a badass Aston Martin, nor did she have Sherlock handcuffed in the trunk.

“The Dying Detective” also found Sherlock giving false infomration to the press on-purpose, which is recreated similarly in this episode: Sherlock pretends to publicly endorse Culverton Smith in order to get what he wants in a long game.

“Killer Orangutan”

When Holmes and Watson are recounting their various adventures to a group of children in a hospital, a story about a “killer orangutan” is mentioned. This is likely a nod to the original story “The Adventure of the Creeping Man,” in which a professor ingests monkey glands and becomes homicidal.

Detecting Footfalls and a Cane

As always, Sherlock Holmes has an uncanny ability to use either footprints of the sounds of footfalls themselves to identify as-yet unseen persons. In “The Lying Detective” he knows Faith Smith is coming because he can hear her distinctive walking pattern and he hears her cane. Identifying people by their footfalls and footprints references The Sign of the Four, while the visage of Faith is reminiscent of “The Adventure of the Crooked Man,” (not be be confused with the “Creeping Man” above!)

Optional Memory Erasure

Culverton Smith’s insidious method of letting people erase their memories at will does not recall a Sherlock Holmes story or novel, but it is reminiscent of showrunner Steven Moffat’s other big property: Doctor Who. In the fifth season of Doctor Who, Steven Moffat wrote an episode called “The Beast Below,” in which Amy Pond (and others) voluntarily erase their memories. This itself was a kind of sideways reference to the story by science fiction master Ursula K. Le Guin called “The Ones Who Walk Away from Omelas.”

Mrs. Hudson’s Shady Past

After her daring exploits behind the wheel of her sports car, Mrs. Hudson mentions she is the ex-wife of a “drug dealer.” This references the first episode of Sherlock, “A Study in Pink,” in which it was mentioned that Sherlock “ensured” that Mrs. Hudson’s late husband was prosecuted to the full extent of the law.

Irene Adler, “The Woman”

Sherlock gets a text from Irene Adler! Appearing in the Season 2 episode “A Scandal in Belgravia,” Adler is of course based on the same Irene Adler from the story “A Scandal in Bohemia.” In both the episode and the story, people think Adler might have been dead. Watson writes of “the late Irene Adler, of dubious and questionable memory.” Many pastiches have given Adler her own adventures, the most famous of which is the series of novels written by Carole Neslon Douglas, which began with her book Goodnight, Mr. Holmes.

Sherlock’s Birthday and More Shakespeare

After Irene Adler texts Sherlock Holmes, Watson concludes that it must be because it’s Sherlock’s birthday. The “joke” of Watson not knowing Sherlock’s birthday until that point comes from the idea that fans themselves arrived on the date for Sherlock’s birthday, since it’s not actually stated in the original stories. Essentially, because the Holmes of the canon quotes Twelfth Night more than once, fans created a complicated reason to arrive at January 6 as his “real” birthday. This episode, “The Lying Detective” aired on January 8, two days after Sherlock’s actual birthday.

Sherrinford Holmes and the East Wind

Mycroft's note about Sherrinford PLUS Sherrinford, revealed.
Mycroft's note about Sherrinford PLUS Sherrinford, revealed.

The shocking ending of “The Lying Detective” finally revealed there is in fact a third Holmes sibling and the person is (probably) Sherrinford Holmes. But, Sherinnford is Sherlock and Mycroft’s sister, not brother. Though not included in the original canon, “Sherrinford” is a long-theorized third Holmes brother and also the original name of the heroic detective before Conan Doyle choose “Sherlock.” In the reality of the show, it appears this Sherrinford is a master of disguise (just like Sherlock) and was also referenced by Mycroft in “His Last Vow,” when both he and Sherlock spoke of “the east wind” a force which destroys everything. When Sherrinford confronts John in the cliffhanger, she specifically references the “east wind.”

Next week, Sherlock Season 4 is set to wrap everything up (somehow) with the finale “The Final Problem,” airing on BBC1 and Masterpiece Mystery! on PBS.

Ryan Britt is a staff writer for Inverse. He is the author of the essay collection Luke Skywalker Can't Read and Other Geeky Truths (Plume/Penguin Random House 2015). His writing has also appeared in the New York Times, VICE, The Morning News, The Awl, Clarkesworld, BN Sci-Fi/Fantasy, Tor.com, and elsewhere. He lives in New York City.