Now that all is said and done, and with a bit of time to mull it over, it's time to discuss the other two episodes of what may well be the final series of "Sherlock." Steven Moffat and Mark Gatiss pull out all the stops as they join forces for the finale. But, let's not get ahead of ourselves.

"The Lying Detective,'' loosely based on "The Dying Detective," has a drug addled Sherlock battling billionaire Culverton Smith, whom he suspects of being a serial killer. "The Final Problem," which also includes elements of "The Musgrave Ritual" sees Sherlock confronting a traumatic episode from his childhood as he squares off a series of deadly puzzles on a lonely prison island.

'The Lying Detective' was a great trick

"The Lying Detective" presented a much-needed step up from the thoroughly conventional and not terribly daring 'Six Thatchers'. Part of this is due to the sheer energy of Toby Jones' performance as the ebullient sadist Smith, who dominates the screen with his hybrid of Jimmy Saville and Trump, but also down to seeing Sherlock in such a state. John Watson is distant, his brilliant mind in a fog of depression and drugs and this is the lowest we've seen the character since Series 2.

John's reluctance and ultimate animosity works well with this, leaving us just as uneasy every time he and Sherlock are onscreen together. They are not quite the old chums and there is a morbid air about them that adds to Sherlock's disconnect from both the world and, seemingly, from reality in his duel with Smith.

Moffat's writing succeeds in keeping us on the edge, toying with Sherlock's deductive abilities and perception, and makes for a great mind game that feels the most playful Moffat's been in years, and without a lot of the self-congratulatory airs of "Abominable Bride."

'The Final Problem' and worthy of it

"The Final Problem" is arguably the most emotional, dramatic and experimental since "The Reinchenbach Fall," and a very strong note to end the whole series on.

Seeing Sherlock, Mycroft and John put through the ringer makes for some intensely engaging Television, as the stakes are raised each time, with the looming prospect of the plane crash acting as a great time bomb to crank the tension higher. Sian Brooke's performance as the lost Holmes sibling, Eurus, is perfect for this episode, straddling the lines between cunning genius and emotionally unstable woman-child as she plays her games.

The ultimate revelation of Redbeard is one of the most effective TV gut punches in recent memory, and the quality of the writing has earned it. It's a testament to the quality of writing when we've seen our leads put in danger many times, yet still feel like they are in genuine peril and that we get more insight into them as characters. A satisfying end to the series 4 and, possibly, the show itself.