Synopsis: In the final episode of this new season, long buried secrets finally catch up with the Baker Street duo. Someone has been playing a very long game indeed and Sherlock and John Watson face their greatest ever challenge. Is the game finally over?
Honestly this season was pretty riddled with plot holes/things that don't add up. It also becomes a bit unbelievable and you lost trust in the plot when there are so many twists and basically anything can happen (eg. Euros literally mentally controlling people).
Synopsis: Sherlock is asked to investigate the mysterious death of a young man, which he solves quickly but he is led into another mystery when a bust of Margaret Thatcher owned by the dead man's father is smashed. Further busts are smashed and Sherlock discovers that the mystery is linked to Mary and her past as a government agent. A figure from her past is bent on revenge in the belief that Mary betrayed him, but it is discovered that the traitor was the secretary of a British Parliamentary member. Mary is killed by the secretary when jumping in front of a bullet meant for Sherlock. John blames Sherlock for Mary's death, and their relationship is fractured.
From the sneak preview of episode 2 here, we see that Culverton is going to emerge as the villain in the next episode. And yet the last time we see Elizabeth in this episode she's sitting right next to a poster of him:
Sherlock ended its fourth season — and possibly its entire series — with the intense “The Final Problem,” which put Holmes and Watson through the emotional wringer, explored the great detective’s mysterious childhood, and ultimately set the stage for a more traditional version of the iconic mystery tales moving forward (should Benedict Cumberbatch and Martin Freeman ever agree to return).
This interview covers some of the scenes in the finale including Molly's, the plane flashback, etc. They don't really reveal much information and leave it pretty open ended as to whether they will come back with another season:
There are no cliffhanging items left over, not that I can think of?
No. There isn’t something we have to come back to address. Which is quite good for us. Because if we do come back, we can j...