[SPOILERS for those not caught up on Sherlock ahead.]
The second episode of Sherlock season 4, was one of the most intense, disturbing and altogether brilliant yet. Sure, there were some faults and weaker moments, but thanks to some great writing from showrunner Steven Moffat, and sublime performances from Benedict Cumberbatch, Martin Freeman and Toby Jones, 'The Lying Detective' has firmly set itself up there as one of the best Sherlock episodes to date.
The acting wasn't the only highlight, though; in a super big plot twist, it was revealed that the third Holmes sibling was in fact a sister, not named Sherrinford, but Euros, and she has been playing mind games with Sherlock and John, masquerading herself as the mysterious 'E' from the bus that embarked upon a text fling with John, as well as Faith, Culverton Smith's daughter who went to ask for Sherlock's help. She also posed as John's therapist, and revealed her true identity in a cliffhanger ending which saw her take aim at John with a gun.
So what's next for the Sherlock finale? Will John end up dying in the same manner as his wife? Well, no, to be honest. He features in the newly-released trailer for 'The Final Problem', which can be viewed, above.
Theories abound as to what the title of the episode could mean, but it now seems likely that Euros will somehow be connected to the final problem that Sherlock faces. In the trailer above, we see Mycroft reminding his younger, seemingly tormented brother, that everything he is today, is connected to his memories of Euros, but where has she been all these years? Why has Sherlock never mentioned her? A glimpse at 'The Final Problem' at the end of 'The Lying Detective', also showed a flashback to Sherlock with Redbeard, his dog. These memories have featured throughout the entire Sherlock series, and could well be the key to unlocking the mystery surrounding the sister.
Viewers who fancy themselves as detectives will have immediately picked up on the fact that Euros said Culverton has delivered Faith's note to her via a mutual friend. With the familiar 'Miss Me?' we always associate with Moriarty, now being used by Euros, is he the missing link? Will Andrew Scott make an appearance in 'The Final Problem', or was Moriarty always just working for (or with) Euros? One final point worth considering; the clue for 'The Final Problem' was Sherrinford, and we know that word or name definitely refers to something or someone that Mycroft thinks is secure. Don't think we've heard the last of that.
Whatever Euros' past, 'The Final Problem' looks to be another tough test of endurance for Sherlock, in keeping with the theme of this season, which has seen the story far more connected to Sherlock and his relationships with those around him than ever before. John seems to be firmly back in Sherlock's corner, and it would be nice to think that Mycroft can be relied upon for a bit of familial support, at least, because it looks like our favorite detective is going to need all the help he can get.
The season 4 finale of Sherlock, 'The Final Problem', airs on BBC 1, PBS and in select theaters on Sunday, January 16.