Sherlock cautiously pushed open the heavy door to the swimming baths and made his way into the interior, keeping his wits about him.

"Hello? I've brought you a getting-to-know-you present."

He held the memory stick aloft.

There was just an eerie silence.

"Come on! That's what it's all about, isn't it? All those puzzles, all those little games were just to divert me from this."

There was another long silence, and then, at last, a creak somewhere to his left, as a figure emerged from one of the changing cubicles. It was John, dressed in a voluminous parka, and he was staring at Sherlock somewhat strangely.

"Well," he said, very slowly, very monotonously, in a dead, robotic voice. "This. Is. A. Turn-up. Isn't. It? Weren't. Expecting. This. Were. You?"

"No," agreed Sherlock, gazing at him, in horror, "I most certainly wasn't. A parka? That's so 1970s. It's a bit of a fashion faux pas, even by your standards. I think I actually preferred the waxed jacket you were wearing in episode 1. And I never thought I'd hear myself say that…"

"No. No." John corrected him, in the same eerily flat tone. "I. Mean. You. Weren't. Expecting. Moriarty. To. Turn. Out. To. Be. Him…I. Mean. Me….Oh. Bugger. I've. Given. It. Away. There. Haven't. I. With. That. Slip. Of. Pronoun?"

"No, it's all right," Sherlock reassured him, "I'd already worked out that John wasn't you, anyway, from his peculiar tone of voice – a bit like a thick schoolchild reading aloud. He's very good, isn't he? All the others have put far too much expression into their voices, so you can tell that they're just actors pretending to be frightened hostages being forced to read out someone else's words, no matter how much they blubber and sob – which they also tend to overdo. That's the trouble with bit-part actors – they will try to milk it and make the most of their moment in the spotlight."

John's only response was to open his parka, a bit like a flasher, and reveal the bomb strapped to his jumper.

"Yeah, yeah, a shitload of Semtex. I was expecting that," called Sherlock to his unseen adversary. "Well done! Did you make it yourself at home, out of old toilet rolls and double-sided sticky tape? So who are you? Reveal yourself!"

"I gave you my number!" yodelled an irritating sing-songy voice from the other end of the pool. "I was hoping you might call."

Gradually, the voice's owner emerged from the shadows.

Sherlock took a step back in surprise.

"Jim? Jim from the IT department at Barts?"

The Irishman scowled. "Yes! And I would have got away with it, too, if it hadn't been for you pesky kids!"

But he seemed to be a creature of changeable moods, because the next minute he was introducing himself in quite an amiable fashion:

"Jim Moriarty, at your service – consulting criminal extraordinaire."

"Consulting criminal? Oh, I get it!" said Sherlock, as the concept dawned on him. "Dear Jim, please will you fix it for me to get rid of my lover's nasty sister, Dear Jim, please will you fix it for me to escape to South America…"

Moriarty grinned. "I'd watch it, if I were you, Sherlock Holmes. You're charting dangerous waters now."

"What do you mean?"

"References to Jim'll Fix It? Please! Do you have any idea how much that dates you? And it will be completely incomprehensible, not only to anyone under the age of about 35, but also to anyone outside the United Kingdom. They'll probably cut that from the PBS version, you know."

"He's right, Sherlock," John whispered a warning through gritted teeth. "They even cut my line about the ASBO from the last episode. Let it go! It's not worth it."

"It's surprising I get the reference myself. I mean, I'm not from the United Kingdom!" Moriarty pointed out, emphasising his brogue, to rub it in."

"Well, you say that," said Sherlock, " but the script is actually ambiguous on that point. After all, you knew Carl Powers when he was a schoolboy in Sussex. That would suggest you grew up in the UK…"

But Moriarty wasn't listening – he'd moved on already. Hands in his pockets, he was glancing around his surroundings as casually as if he were a househunter surveying a possible property which he'd already decided lacked the Wow! Factor and failed to tick all the boxes.

"Well, well," he said, "here we are, back at the old pool where it all started, where dear Carl died."

A look of ugly hatred flitted across his face.

"Carl Powers!" he muttered. "He used to laugh at me. He used to make fun of me for my squeaky voice, which he said was kind of a cross between Graham Norton and Joe Pasquale…"

"Well, you've got to admit, mate, he did have a point," Sherlock interjected.

"I stopped Carl," yodelled the Irishman, as if Sherlock hadn't even spoken, "and I can stop Johnny Boy here, too, if I want to. Stop his heart."

With a sideways move of his head he gestured to the red laser point hovering on John's chest.

Sherlock suddenly felt a lurching sensation in his stomach. For the first time, he confronted full-on the truth of how much John had come to mean to him.

But Moriarty had made a bad move. Calling a burly ex-soldier "Johnny Boy" was just asking for trouble. Before anyone had time to bat an eyelid, John had Moriarty in a half-nelson, cleverly using him as a human shield to guard himself from the unseen sniper, and was shouting "Run, Forrest, run….er, sorry, I mean, Sherlock …"

But Sherlock was a bit slow off the mark and before long the moment had passed. The sniper's sights were now set firmly on him.

Moriarty writhed free from John's grasp and brushed down his suit, glancing at Sherlock's sidekick reproachfully.

"Careful!" he said. "Matalan. We could both get a nasty electric shock if the polyester gets chafed too much. BBC cuts, you know."

Sherlock nodded. "That's also why they've sent us to this dilapidated swimming pool in Bristol. The location budget didn't stretch to the Reichenbach Falls."

"I'm warning you, Sherlock Holmes," continued Moriarty, pressing his advantage, "to stay out of my affairs. I've had enough of you meddling in my plans, ruining my best-laid schemes…"

"That's not strictly true, though, is it?" Sherlock pointed out. "I mean, I haven't really been meddling in your affairs. Quite the reverse, in fact. You keep following me round like a particularly tenacious stalker, dangling your business in my face. Like in A Study in Pink, I was nowhere near solving the case – I kept missing the blatantly obvious fact that it was the taxi driver, a fact which, quite frankly, a five-year-old could have deduced, so you helpfully sent him round to my flat to point it out to me. Then you sent me my own mobile phone, a lovely pink colour to coordinate with my Princess Barbie and my My Little Pony, just so you could inform me of all your cold cases and then kept dropping hints to help me solve them. You're a bit like one of those smartypants bastards who sits next to you on the Tube, reading the crossword clues over your shoulder and telling you all the answers before you've had time to work them out yourself."

Moriarty's eyes narrowed and he moved his neck from side to side like a lizard about to strike its prey.

"Just you wait, Sherlock Holmes! You may think you've outsmarted me, but just wait – if we ever both get invited to the same offal-themed barbecue and I get let loose on the apron and tongs, then I'll have my revenge!"

Sherlock smirked. "Oh, yes? What are you going to do? Undercook my sweetbreads? Add too much spice to the marinade for my devilled kidneys?"

"No! I will BURN YOUR HEART!"

That wiped the smile off Sherlock's face. He liked his offal rare. He made a mental note to avoid any barbecues in future where they might put a psychopathic Irishman in charge of the charcoal.

Still, he tried not to show how unnerved he had been by this threat.

"Yeah, right!" he blagged. "You're all mouth and no trousers, Jim! If you wanted me dead, why didn't you bomb my flat, not the gaff over the road? Why didn't you get the taxi driver to shoot me in the head instead of going into all that preposterous rigmarole with the two pills? Why didn't you tell your snipers to shoot me the minute I walked in here, instead of doing your extended James Bond villain routine?"

Moriarty turned positively puce with rage. "Stop it, Sherlock Holmes! You have no idea of the scale of evil with which you are dealing…"

"Oh, and that's another thing, why do you keep calling me 'Sherlock Holmes'? It's like the aural version of those lazily computer-generated letterheads where they can't be arsed to call you 'Mr Holmes', because it's too difficult to manage in Mail Merge. Tell you what? If I promise to always call you 'Jim' or 'Moriarty' or 'Mr Moriarty', will you call me a proper name in return?"

But there was no response, other than a rather rude talk-to-the hand gesture, as the evil criminal mastermind slipped away as suddenly as he had arrived.

Sherlock breathed a sigh of relief, but he knew not to get complacent. He wouldn't truly be able to rest easy until he'd removed John's suicide vest and thrown it to a safe distance of about 150cm. After all, the last Moriarty-constructed vest that went up had blown up an entire block of flats and killed 12 people distributed over an area of about 100 square metres, so pushing the vest about three feet away was a sensible precaution.

"Well, John," he said, breathlessly, once he'd pushed the vest arm's length away. "Moriarty's buggered off, but I'm not sure about his sniper henchpersons. Wouldn't it be a good idea to get the hell out of here?"

"What's the rush?" shrugged John, sitting down for a breather. "Why don't we hang around for a bit and engage in a little light homoerotic banter?"

"Good idea! Listen, you know that thing you did, jumping a volatile psychopathic criminal mastermind when I was still in full view of his sniper? That was….good."

But they weren't allowed to enjoy a little post-watershed flirting for long, because almost immediately they heard the slam of the door reopening and a sickening "Cooee!" from the other end of the baths.

"Sorry, boys! I'm sooo changeable. I'm one of those annoying bastards who waits until they've got to the very front of the queue at McDonald's before even starting to consider whether they want a Big Mac or a Filet O' Fish, they hum and ha for about five minutes, then just when you think they've finally made up their mind and placed their order and the girl behind the counter starts bagging it up, they say 'You know what, love? On second thoughts, scrub that - I'll have a McChicken Sandwich and a Crunchie McFlurry'."

John blanched. Yes, he'd been behind one of those arseholes in the queue in McDonald's and he had to agree – that was, indeed, the ultimate human evil.

"I'm afraid, boys, you cannot be allowed to continue."

All of a sudden, Sherlock and John felt the heat of multiple lasers trained on their faces and bodies. The snipers suddenly seemed to have reproduced, as if by binary fission.

"Oh, I think we can," said Sherlock, studying his nails in an unconcerned fashion. Then he flashed Moriarty a patronising smile. "They're already in negotiations for a second series."

"In negotiations, yes, but it hasn't been confirmed!" Moriarty taunted them, triumphantly.

"Still, they're not going to let you kill us off yet. They're going to wait and see what the first series' viewing figures are like."

"You think?"

"I know!"

Sherlock underlined the steely finality of these words, by aiming his gun at the discarded Semtex which he'd so enjoyed removing from about John's person.

Moriarty looked distinctly disgruntled at this, but then he had a lightbulb moment, as a cunning plan occurred to him. "Maybe so…but they can't stop me leaving you on an awkward cliffhanger!"

Suddenly Sherlock felt himself frozen to the spot, his face stuck in an intent stare, as if he had been pulling a silly face when the wind changed direction, his arm stretched out in front of him, pointing his gun at the Semtex.

Jim was also frozen, his face fixed in an arrogant smirk.

Sherlock was paralysed, so he couldn't turn and look, but he knew with a depressing certainty that, behind him, John would also be rooted to the spot, a gormless look on his face, his mouth open in an expression of horror.

What a bummer! They were going to be stuck like this for the next twelve to eighteen months – longer, if Mark and Steven got tied up in their work on Dr Who. It was going to be a very long wait and already his arm was getting tired.