At the start of a couple of the old Rathbone & Bruce Holmes films there’s a screen-card which describes Sherlock Holmes as “the immortal character of fiction… ageless, invincible, and unchanging”.

And it’s true. He is. Not even his creator Conan Doyle could kill him off. The public wouldn’t allow it. Because, like Batman or Colonel Sanders, Sherlock is more than a man, he’s a symbol, and you can’t kill a symbol…

…can you?

We all know what happens at the Reichenbach Falls in The Final Problem, and writer Steve Thompson knows we know. It’s the day Holmes appears to die, and the day the ‘Napoleon of Crime’ meets his watery Waterloo. But such have been the novel twists and extrapolations on Holmes lore by the Sherlock team across both series that you’d be a fool to think The Reichenbach Fall would be so simple.

As Jim Moriarty, Andrew Scott channels his inner Joker with tremendous glee. All malevolent gurning and tantrums, in one tense scene with Sherlock he’s just one lick of the lips from Heath Ledger’s famous “See, to them, you’re just a freak… like me”. And as the indestructible object of Moriarty’s depravity meets the immovable force of Sherlock’s genius, you quickly realise that whatever happens, these two men are bound together on an ineluctable course.

The consulting detective and the consulting criminal; two sides of a coin still in mid-flip. And this is the episode where the penny drops.

Moriarty sits, spider-like, at the centre of his giant web, and this time he’s spinning a trap around our dear detective. The devious strands are at first, too fine to see, but all too soon you can discern the trap coalescing, and woven into it are Holmes references of all hues, shades of The Dark Knight (and not just because of Cumberbatch’s flappy cape of a coat) and even Steven Moffat’s own recent adventures with the Time Lord.

In all this Sherlock bears his burgeoning humanity like a wound, and though Series 2 has been about Cumberbatch taking Holmes into the uncharted areas of his own amygdale, let’s not forget Martin Freeman’s superb and consistent portrayal of Dr. Watson, which has never been stronger, nor more moving, than it is here.

John Watson, the loyal companion and soldier, who’s seen so many comrades fall on the battlefield… will he see his dearest comrade fall too? What does that even mean, ‘fall’? That’s the real question you want to ask yourself going into this episode. Going out you’ll have a much bigger question.

But we’re not going to touch on the final act, which will have you on the edge of your seat, then falling off it, then clambering back on, only to find yourself placed even more precariously than before.

This is an episode that many will be undoubtedly be watching again… and again… desperately searching for the clues, because surely, as Sir David Frost used to say on Through the Keyhole, “the clues are there”. Or maybe the game afoot is one that’s playing us all for fools.

This is shocking, emotional and damnably clever television, and whatever happens, Sherlock’s second run has been so monumentally strong that history is bound to repeat itself. The public, just as when the last page was turned on The Final Problem, want more.

So Mr. Moffat, Mr. Gatiss, Mr. Thompson; please, give it to us. Just please don’t make us wait another year and a half.

Airs at 9pm on Sunday 15th January 2012 on BBC One.

> Order the Series 2 DVD on Amazon.

> Buy the Series 1 DVD on Amazon.

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