They're finally back for a proper season, rather than a weird one-shot mixed in with a period drama, and they are certainly not holding their punches back. Season four comes roaring out of the gate with The Six Thatchers, which promptly pushes the mystery of Moriarty to one side and focuses on the character's developing relationships. Watson has a full family, one of whom we now know is a highly trained assassin capable of keeping up with all but Sherlock's most ridiculously intricate plans. It's a lot of fun watching Mary juggle motherhood whilst still finding time to indulge her intellectual side with Sherlock. It's also sad, yet clever, to begin playing on our emotional heartstrings as John's infidelity comes to light and Mary's past starts to unravel. The result is a classic Sherlock episode, filled with intrigue, incite into human nature, suspense and mind games. And then it culminates with a gut punch that suddenly throws everything up until that point into stark contrast.

There are few series around today that will end the first episode by killing a major character that had rapidly become a fan favourite, but Sherlock is still a league ahead of most series around today. It was a painful but very well executed moment of television that, personally, deserves serious applause. How much it was predicated by Moffat and Gatiss genuinely planning to remove her from the show or whether the IRL split of Freeman and Abbington made it a preferential route, I doubt we'll ever know. The result, though, was exceptional and led very nicely into The Lying Detective.

The general consensus amongst my friends and selected media bubble is that episode two was the only one worthy of the Sherlock brand. My words on episode one above probably show that I don't overly agree with this sentiment, but the following will finalise that message. Personally, The Lying Detective was the weak rung in the ladder of season 4, acting more as a self-contained loop of filler than anything bordering true character development or progression. The central concept is one we've seen before and it felt recycled as a result: Watson is pissed at Sherlock, Sherlock must solve a case to heal the wounds. There are some neat moments, particularly the use of Mary's 'ghost', both in Watson's delusions and Sherlock's more tangible pre-recordings. These achieve the closure that her character both requires and thoroughly deserves. Plus, the core mystery is an interesting one, positing that with enough wealth and influence a serial killer could simply become invisible to society. There are clear parallels with the real world revelations about high profile British paedophiles in the last few decades, which results in some interesting thought experiments being enacted. Overall, The Lying Detective achieves what it needs to by sealing off the pain from episode one and setting up the antagonist for episode three. That it also does so whilst twisting and turning all over the place, in true Sherlock fashion, with some neatly timed editing and excellent dialogue is practically par for the course. It is by no means bad television; most shows would count themselves lucky to produce an episode this strong. But still, personally, it feels a little tired and repetitive.

Neither of which phrases can really be applied to The Final Problem. I do understand why many Sherlock fans felt a little miffed that this was both the season's grand finale and the answer to the Moriarty problem. Whilst I agree having his "return" be nothing more than an orchestrated manipulation using pre-recorded sound bites (a bit of a theme for season four; even the first episode had a sub-plot involving one) is a little less exciting than had he strolled out onto the lawn of Buckingham Palace, it would also have been pretty hard to explain. We saw Moriarty die. There aren't many ways you can argue your way out of that which wouldn't feel like a cop-out and, personally, I feel his presence was used to good effect. His image and association lend a sense of meaning to Eurus's purpose which is hard to explain.

I also understand that The Final Problem isn't really a Holmesian mystery. It's more a character dissection (or vivisection, to quote Holmes himself) allowing the viewers a much greater look into the core of these beloved fictions. It is brilliant fun to finally have an excuse to pit Holmes against Holmes and adding a third Holmes into the mix just ups the stakes. Letting Mycroft get some personality and genuine screen time is refreshing as is his utter lack of ability to cope with what's happening. The aircraft metaphor was a little forced, but it worked well enough and it is immensely refreshing to have a sympathetic antagonist. So far, the only people on the Sherlock universe that could even come close to matching the titular character for wit and intelligence have been monsters, most of whom live amongst us camouflaged from our view. Eurus is their polar opposite, someone who has been confined and hidden from society for her entire life, feared and revered equally, but yet her yearning and desire isn't some awful evil. She just wants forgiveness, empathy, friendship. She understands, somewhere in her psyche, that her manipulation and childhood crimes are wrong but they're a path she feels trapped on, reinforced by her living conditions and assigned place in society. She is an incredible meta-analysis of the show in its entirety, literally flipping the usual messages on their head and blurring what remained of the lines of morality. I thought she was incredibly effective and, by the final curtain, one of Sherlock's most inspired creations.