Warning: The following review contains spoilers.

Sherlock is over so quickly isn’t it? One week you’re celebrating its return and less than a month later, you’re waving it bon voyage. And after the last two weeks of plotting, it’s no surprise the fervour people had for this – the final episode of Season 4 and, potentially, the last episode of Sherlock for a very long time.

It’s little wonder that creators Steven Moffat and Mark Gatiss, writing together as they did for The Abominable Bride, wanted to give their supporters something to wave their flags to. Think of The Final Problem as the Greatest Hits of Sherlock, with choice cuts of your favourite moments repackaged into a handy 90-minute feast. Sadly, as pleasant as it is to see the two writers clearly having fun in their sandbox, the real problem for the viewer was trying to work out how the two previous episodes could justify such a lukewarm finale.

Having revealed a third Holmes sibling and putting the life of John Watson (Martin Freeman) in danger last week, we were given a rather rushed resolution as to the Doctor’s fate.

Apparently, Eurus (Sian Brooke), Sherlock’s evil sister, had merely stunned Watson and run away. An impossibility according to brother Mycroft (Gatiss) who insisted that she was trapped within a super-prison by the name of Sherrinford which was stuck on an island out to sea. All of which was a massive surprise to Sherlock, who had completely forgotten he’d ever had a sister. If that part sounds like a tough pill to swallow, The Final Problem produced a number of other headscratchers that unfortunately lowered the plausibility of its narrative.

Things started off strong with a small girl waking up on a plane in which all its passengers and crew had passed out. Answering a ringing phone in the hopes of calling for help, she’s greeted by the voice of the late consulting criminal, Moriarty (Andrew Scott). Elsewhere, having escaped the detonation of 221b Baker Street – another one of Eurus’ games – the Brothers Holmes and Watson break into Sherrinford to understand how the meddling sister is able to break out.

Before continuing, it should be noted that Sherlock has dipped its toe in the surreal before. Season 2’s The Hounds of Baskerville, for instance, attributed its hell hound to psychotropic gas. Indeed, the very idea of Sherlock himself is a flight of fancy in the real world. However, The Final Problem was something else.

As well as being superior to her brothers intellectually, Eurus was shown to be able to ‘reprogramme’ those around her and, as such, had unbelievably managed to take over her own asylum, giving her free passage to leave her island prison as and when she felt like it. Spurred on by a meeting with Moriarty several years prior – in a hilarious cameo by Scott –  she had decided to take her vengeance out on Sherlock for reasons that never feel satisfactory. Over the last few seasons, a lot has been made of the name Redbeard and its influence on Sherlock’s persona. Previously thought of to be a beloved pet, the final twist turned out to be something much sinister and had led to Eurus’ incarceration. Gatiss and Moffat try to turn what would be a childhood trauma for Sherlock into a reason for his thirst for solving mysteries. But as an attempt to give Sherlock back his humanity, it just didn’t convince.

Neither did the system of Saw-like problems Eurus put her siblings through, with a different room in Sherrinford leading to a new and deadly conundrum. As Eurus pulled her brothers’ strings, the continuing train of thought was ‘How can she afford to do all this? Literally, who is funding this person?’ and ‘Does anybody remember John had a baby daughter?’ When the girl on the plane was revealed to be Eurus in a mind palace of her own waiting for Sherlock’s approval, The Final Problem revealed itself to be trying too hard.

Thank heavens then for the positives that didn’t make this a complete washout. Take for example Molly, played by Louise Brealey. Criminally underused this season, Brealey brought much needed emotion in a scene that saw her bare her soul to Sherlock, whilst being an unwitting pawn in Eurus’s schemes. As we cheer on Sherlock’s sociopathic qualities, we often forget how they can deeply cut others. It was a wonderful moment, only somewhat surpassed by Mrs Hudson thrashing around to Iron Maiden in her slippers.

As the dust settled, Sherlock ended, as perhaps it was always going to, with a massive press of the reset button that allowed Gatiss and Moffat to bring a close to their 6-year story in a deserved self-congratulatory tone, whilst tentatively leaving the tiniest of margins for a possible return. And whilst this wasn’t the ending some of us will have been expecting, the journey to get this far has at least consisted of more highs than lows, with a heavy vein of experimentation throughout. For that reason alone, Sherlock is still, as a whole, a quality British drama.