Seriously. Do not scroll down until you have watched the end of the Sherlock episode "The Lying Detective".
At the end of the episode, we found out that the woman who Watson (Martin Freeman) was sending flirty texts to...
...had been wearing a disguise and pretending to be Watson's therapist...
...AND pretended to be Culverton Smith’s (Toby Jones) daughter, who Sherlock thought was a drug-fuelled hallucination.
So all the women were one person and that person happens to be...Sherlock's sister!
At a Q&A following a screening at BAFTA Cymru in Cardiff, Sherlock co-creator Steven Moffat talked about Watson's fling in the first episode: "With mystical inevitability it was Sherlock's sister!"
The shock twist scene, when her true identity was unveiled, has been an idea ever since Moffat and Gatiss were making “His Last Vow”. That's the episode where Charles Magnussen is shot by Sherlock.
The biggest shock in last week's episode, "The Six Thatchers", was not just Mary's (Amanda Abbington) death, but also Watson being a bit of a dick by having an affair AND blaming Mary's death on Sherlock.
Gatiss added that Watson has not yet overcome the devastating circumstances surrounding Mary's death.
And then there's the staggering twist that Mrs Hudson (Una Stubbs) was the one driving the car at the start of the episode, which had Sherlock in the boot.
Moffat also talked about Gatiss writing a poem to The Guardian in response to a column in the paper about the show turning into something too much like the Bond films.