Sherlock's season four finale went all out to blow the socks off its audience, as it delivered an action-packed 90 minute climax that threatened the lives of just about all of our favourite characters at one point or another. It is an episode that has proved controversial with fans, even though pretty much all are praying it won't turn out to be the final ever episode of the show, as showrunners Steven Moffat and Mark Gatiss have threatened.
With Sherlock, John and Mycroft trapped in an underground facility at the whim of a psychotic inmate, it was more like a horror or action movie than Sherlock has ever been. And, whatever you thought about it, it was certainly very far removed from the traditional armchair detective stories written by Arthur Conan Doyle.
While it might have been of a very different spirit to Doyle's work, however, The Final Problem was still stuffed to the rafters with nods and references to the original Sherlock Holmes stories - along with a few callbacks to some other bastions of pop culture.
Read on for 20 easter eggs you might have missed in the season - series? - finale of Sherlock.
20. Mycroft's Portrait
During Sherlock and John's elaborate prank on Mycroft at the start of the episode, he becomes spooked after the portraits on the walls weep blood.
One of these portraits looks a lot like Mark Gatiss in Elizabethan dress, presumably intended to be an ancestor of the Holmes family. This recalls a plot point in The Hound of the Baskervilles. Holmes realises that Jack Stapleton is in fact a member of the Baskerville family due to his uncanny resemblance to one of the portraits hanging in Baskerville Hall.
If you were wondering who the man in the clown suit and the dwarf woman dressed as a child in this scene are, Sherlock tells them to collect their money from Wiggins and "don't spend it all in one drug den." Presumably, then, they are members of his Homeless Network.
For more on Wiggins, read our easter eggs list for The Lying Detective.