Sherlock is known for its surprising twists and turns, and "The Lying Detective" served up several shocks to the audience on Sunday. Beware, as there are SPOILERS ahead relating to the Season 4 episode of Sherlock, "The Lying Detective." It's long been speculated that Mycroft and Sherlock Holmes have another sibling, who's usually referenced as a secret brother. However, Season 4, Episode 2 of Sherlock finally revealed the truth about the detective's familial connections. Sherlock revealed that there's a Holmes sister.
Back in July 2014, there was huge internet speculation that Tom Hiddleston would appear in Sherlock in a very special role, as the third Holmes sibling. While that rumor didn't pan out, the story line finally came to fruition in "The Lying Detective." The Conan Doyle story that the episode references, which is sometimes called "The Adventure Of The Dying Detective," was originally published in 1913. In the story, Holmes fakes a fatal illness to ensnare a confession from the antagonist who is responsible for a murder. The original story makes no mention of a brother or sister of Holmes, but as the BBC's Cumberbatch version of the show tends to do, the episode went in a very unusual direction. And as it turns out, Sherlock Holmes has a sister.
One of the reasons fans were so amazed by the revelation that Sherlock has a sister, is that the character actually appeared in the first episode of the season, "The Six Thatchers." It turns out that Sherlock's sister is somewhat of a chameleon and has been playing several characters under our noses simultaneously. Perhaps, most importantly, Sherlock's sister was the woman on the bus that John Watson started a texting affair with in Season 4, Episode 1.
Sherlock's sister also appears early on in "The Lying Detective" as a woman who visits Sherlock to give him his next case. She pretends to be Culverton Smith's daughter, but later, Sherlock realizes that it was a different woman that had come to see him. And it's not until the end of the episode that it's revealed that Watson's female therapist is the very same woman wearing a gray wig and contact lenses, and she's holding Sherlock's companion at gun point.
Sherlock's sister is called Eurus, which means east wind in Greek, a reference to the Arthur Conan Doyle story, "His Last Bow." However, Conan Doyle makes no mention of a sister, and the east wind is merely mentioned in a discussion about the weather between Holmes and Watson. It's interesting to see that the show's writers have drawn inspiration from the source material in this way, though.
Clearly, Sherlock's sister, Eurus, is going to play an important role in the next episode of Sherlock, especially as she's holding Watson captive.