Three words sum up The Reichenbach Fall following its conclusion: ‘how the hell?’ And they are immediately followed up by several more: ‘When is series 3?’

Loosely based on Arthur Conan Doyle’s The Final Problem – the story notorious for killing off Sherlock Holmes (albeit temporarily) – some viewers may think they know exactly what’s coming and believe they have it all figured out. Indeed the episode, seemingly playing to these expectations, immediately opens with a scene that appears to confirm the world’s greatest detective is dead. But of course it’s not going to be that simple.

The episode then jumps back in time three months. Sherlock is alive and well and he’s become even more of a celebrity for his exceptional crime solving abilities (not that he likes it, mind). It’s not long before nemesis Jim Moriarty is making headlines of his own when he sets into motion a series of incredibly audacious crimes.

Moriarty was just showing off. What the criminal mastermind really wants to do is “solve the final problem.” One last game to prove he’s beaten Sherlock before finishing it once and for all. Just killing your rival this time would be boring though; better to destroy his reputation and shame him first. So Moriarty poses question that no one has asked yet – could Sherlock actually be a fake; is he really a genius or has he pulled a magical act on everyone? You will perhaps begin to question it yourself throughout the course of the episode.

Obviously Andrew Scott is given a much bigger role than ever before. Scott’s portrayal of Moriarty certainly divided opinion when he was revealed in the Series 1 finale. But it’s been hard to judge him fairly as his screen time, up until now, has so limited. Thankfully, his character is fleshed out and Scott delivers a more balanced performance here. Well, about as balanced as playing a psychopath can be.

It goes without saying that Benedict Cumberbatch is marvellous. We’ve seen different sides to the cold and emotionless Sherlock this year. Love and fear were explored in A Scandal in Belgravia and The Hounds of Baskerville respectively. When Sherlock goes up against Moriarty, he not only faces his evil equal, but also his own mortality.

As for John Watson, Martin Freeman’s best scenes come in the shocking final act where he delivers an understated and incredibly moving performance. Unfortunately, it’s impossible to elaborate without spoiling.

Steve Thompson may be the black sheep of the Sherlock writing trio, but fortunately, he delivers a script that is on par with his peers. It’s not quite as witty as previous stories, but then the episode tone is a darker overall.

This is the first episode of Series 2 not to be have been directed by Paul McGuigan. Doctor Who’s Toby Haynes picks up the reins admirably though. The same stylish visuals we’ve come to expect are all present and correct and Haynes injects few of his own tricks for good measure.

The Reichenbach Fall is a rollercoaster ride full of twists and turns, genuine shocks and a killer final scene. It completes another brilliant, if all too brief, series of Sherlock.  More please BBC, sooner rather than later.