Entering the flat one fine, autumn morning, John was stunned to find his normally ebullient flatmate sitting on the sofa in the depths of despair, his head sunk wearily into his hands.

"Anything wrong, Sherlock?" he probed, tentatively.

The other man groaned.

"I've been such an idiot, John! How could I have missed the pattern in the clues that have been mounting up for the last few weeks? All autumn they've been staring me straight in the face, but I've only just picked up on it. Those break-ins of Moriarty's had absolutely nothing to do with a computer key code. No, they are part of his most audacious plan yet: a plan to turn the United Kingdom into the 51st state of the USA!"

John's eyes widened like saucers.

"But….but…that's impossible!" he spluttered.

"I wish it were, John, I wish it were!" Sherlock murmured, shaking his head, wryly. "But, sadly, owing in part to my asinine lack of vigilance, he's achieved an alarming amount already. He's already managed to abolish the laws prohibiting the possession of handguns and have mortuaries renamed 'morgues'. Then, last week, I was testifying at a criminal trial at the Old Bailey (although, come to think of it, I have no idea why, as surely my testimony that the defendant once held me at gunpoint and threatened to blow me up with a suicide vest would have been totally inadmissible as evidence in a trial for a completely unconnected series of burglaries, but that's by the by) and even I found myself referring to 'objections' being 'upheld' or 'overruled' by the judge! He's penetrated our legal system now, John! And it's getting much more serious: the break-in at the Bank of England was clearly the first step in his plan to replace the pound with the dollar…"

"Ah," said John, catching the drift. "And the Tower of London raid was an assault on the symbols of monarchy, helping to pave the way to the replacement of the Queen with an elected President. But what about Pentonville prison? Why would he want to break into that?"

"Isn't it obvious?" said Sherlock, gesturing wildly in frustration. "He broke in, in order to install a lethal injection chamber. He's restoring capital punishment to the UK!"

"Oh, no!" gasped John.

"Oh, yes!" sniggered a familiar voice behind them.

It was the man himself, who had managed to sneak up the stairs soundlessly by attaching Mrs Hudson's dusters to the soles of his shoes and taken them by surprise. His slight form was now framed in the doorway.

"That's right, Sherlock, " he smirked. "I'm acting in cahoots with your other archenemy, The Daily Mail, on that one. Capital punishment! There's nothing their readers would like more than to see criminals, illegal immigrants and women who appear naked in television dramas before the nine o'clock watershed hung."

"Hanged!" John and Sherlock chorused, almost on auto-pilot.

"I suppose there's no point asking you why you're doing all this?" Sherlock added, wearily. "It's just a game to you, I suppose. Just more of your evil, motiveless machinations."

"Motiveless? No, my machinations may be evil, but they're not motiveless, at all. Didn't you know? It's the Irish Spring."

Sherlock quirked an eyebrow, because that's what people do in fan fiction.

"The Irish Spring?"

"Yes, Sherlock. A bit like the Arab Spring, except it happens in the autumn. And there's Irish people. Oliver Cromwell? The Potato Famine? Easter 1916? You thought we'd forgotten? Well, we hadn't and now it's payback time! We owe you. Now it's you guys' turn to know what it feels like being under the oppressive grip of a colonial power for several hundred years!"

Sherlock let this all sink in. He said nothing for several moments, but, in that time, his face seemed to age twenty years. He looked utterly, utterly broken, as if he'd been working through all the options in his head and had come to the conclusion that he had, at last, reached checkmate and the only feasible outcome was to enter his own personal Gethsemane.

"Goodbye, John," he said, at length, shaking his friend's hand, stiffly, a stoic exterior thinly veiling his emotional trauma. "Thanks for all the homoerotic subtext. It's been….good. And tell Molly from me that she's not really an annoying little drip."

Then, noticing John's incredulous expression, he conceded, "Yes, I know that's not true, but I have to start being nice to people now. My character trajectory outline says so."

He stood up, his face set in the fixed mask of a man who has determined to set himself on the path of martyrdom and will not let himself turn back.

"All right, Mozza," he said, with a grave nod. "Let's go up to the roof terrace now. I'm ready."

Moriarty looked baffled.

"Roof terrace? What are you talking about? Ready for what?"

"To jump off a high building. Isn't that what this has all been about? Me having to sacrifice myself in order to save my friends from a fate worse than death?" His voice dropped to a whisper. "But one last request, eh? Let me wear the coat when I go? It's such a babe magnet."

Moriarty looked amused.

"Die? I don't want you to die! Whatever gave you that idea? No, I want you to carry on living and experience the humiliation of having to call a toilet a rest room, not having universal health care and always having to tip waiters 20%"

Sherlock was totally flummoxed.

"But that's why this episode is called The Reichenbach Fall, right? 'Fall', because I fall off a high building, and 'Reichenbach', because of some confusing and not terribly interesting subplot about a stolen painting which I didn't quite get?"

His arch-enemy burst out laughing, unable to believe his luck.

"No! Don't you understand? My evil plans have progressed so far that I've even been able to infiltrate the title! It's called The Reichenbach Fall because it's set in the autumn!"

Sherlock's face turned to whey and he clasped his hands to the face as if he were imitating that painting by Munch.

"Noooooooooooo!"