A melancholy Chinese folk tune, played on mournful bamboo pipes, filled the air, setting the scene for the events that were about to unfold. It was atonal, monotonous and was starting to do everyone's heads in, but they had to leave it on a permanent loop to drown out the noise from the extractor fan.

At Mr Woo's £5 All-Inclusive All-You-Can-Eat Chinese Buffet on the Kilburn High Road, Yu-No Hoo was giving the other staff a demonstration of the ancient oriental art of ornamental paper napkin folding.

"A serviette is like a person!" she warned, in the melodramatic, mystical tone that people normally adopt when they are imparting cutesy bits of life coaching advice. "You cannot keep it in a box forever! It needs to be taken out and handled."

As if to demonstrate this, she shook a bunch of serviettes out onto the table and began folding them into all sorts of clever shapes – a crane in flight, a water lotus, a traditional Chinese fishing boat, and a novelty penis-shaped one that always seemed to go down a treat when they had a hen party in.

"Serviettes need human company!" she intoned. "They only come alive when they feel a human touch! They might claim that they're perfectly happy staying in their box, all on their own, but really they are terribly lonely. They need people to reach out to them. They need friends. They're frigging bored, OK?…"

She had a feeling that she might be slightly losing the thread here, but it didn't matter, as nobody was listening anyway, apart from Joey, the spotty boy with the Saturday washing-up job who had a bit of a crush on her and spent most of his shifts staring at her tits.

Glancing at her watch, she realised that she had five minutes before lunchtime service began. She might as well nip to the loo while she had the chance.

No sooner had she locked herself in the staff cubicle than she noticed it. Something monstrous. Something that made the half-digested remains of her lunch curdle in her stomach. And, no, Joey hadn't done one of his monster number twos and then forgotten to pull the chain again. It was even worse than that!

Meanwhile, a few miles away, in a dentist's waiting room off the City Road, Sherlock was anxiously awaiting his check-up. He'd taken John with him to hold his hand, but having a muscular ex-soldier sitting next to him had done nothing to still his nerves while he grappled with his fear of fillings, needles and anaesthetics. The only up-side to the situation was that the dentist's waiting room was the one place on earth where he could read Heat magazine in public without people thinking he was a chav.

Suddenly, an ear-shattering scream pierced through the surgery. Sherlock looked up reluctantly from an article about Jordan's latest breast enhancement. Was someone having root canal treatment?

But, no. It was the dentist herself who came running into the waiting area in some state of distress.

"Something the matter?" asked Sherlock, raising an eyebrow, quizzically.

"No, I am not looking fatter!" responded the dentist, rather indignantly. "I've just lost seven pounds with Celebrity Slim, actually."

"You'll have to speak a bit louder, love," said the receptionist, helpfully, glancing up from her nail filing. "She's a bit deaf. It's all that drilling. Plays havoc with your eardrums."

"IS THERE A PROBLEM?" bellowed Sherlock. "I'M A CONSULTING DETECTIVE. MAYBE I CAN HELP?"

"IT'S THE PORTRAIT IN MY TREATMENT ROOM!"

"No, YOU don't have to shout! I don't have hearing problems…"

"THE ONE OF THE DENTIST WHO FOUNDED THIS PRACTICE. SOMEONE'S SPRAYED GRAFFITI ALL OVER IT!"

Realising that everybody else in the waiting room would soon be deaf, too, if they were subjected to the dentist's shouting for much longer, John and Sherlock followed the white-coated woman into her treatment room, where she pointed at a portrait on the wall of a stern-looking gentleman in turn-of-the-century dress.

The painting had been utterly desecrated by a graffiti artist using shocking pink paint. It was now wearing a pair of fluffy pink ear muffs, had a pair of devil's horns on its head, a torrent of snot flowing out of its nose, joke shop spectacles and moustache, as well as comedy breasts and penis. Sherlock shook his head. Some people just didn't know when to stop. Additionally, the numbers 34 and 15 were scrawled on the wall either side of the painting.

"I don't know how it happened!" sobbed the dentist, clearly still distraught. "I only turned my back for about thirty seconds, to wash my hands and mix another batch of dental cement, but when I turned round again, there it was!"

"And was there anyone else in the room at the time?" asked Sherlock. "Perhaps they could shed some light on it?

"Well, there was my patient, Mr Van Mann, but he wouldn't have done it! He's a banker. I mean, if he's in an anti-social frame of mind, why would he bother defacing one piddling painting when he's got the opportunity to wreck the whole bleeding economy?"

"Why, indeed?" thought Sherlock. No, he could rule out the banker as the perp, but he might have seen something.

"And where's Mr Van Mann now?" he asked.

"Oh, he's still in the…" The dentist faltered, and looked around, puzzled. "That's odd. He seems to have disappeared."

"Not to worry!" said John, brightly. "I'm sure we can run him to earth in no time. What's his full name?"

"Wight Van Mann."

Sherlock grinned. This should be easy. Not many of them in London.

"Address?"

"Oh," she murmured, vaguely. "I'm afraid you'll have to ask the receptionist about that. She's the one that keeps all the records."

But by the time Sherlock had and John had navigated the surgery's antiquated filing system, deciphered the receptionist's abysmal handwriting and hot-footed it to Van Mann's loft apartment in Shadwell, they were too late. The flat was sealed off with police crime scene tape and a stroppy plain clothes detective refused to let them in.

But through the open doorway, which gave onto a cavernous, open-plan living space, they could see the body of a man lying face down on the floor by the sofa. He'd obviously not long been out of the shower, as he was dressed only in a towel, revealing the fact that he had a huge tattoo of a dragon across his back. Ominously, he also had a gaping bullet hole in the side of his head.

"Nothing much more we can do here," the investigating officer was saying to his sergeant. "Obviously a tragic suicide. We'll have to get onto informing the next of kin…"

"Wrong!" scoffed Sherlock, ducking under the police tape and striding into the flat, before the constable had a chance to stop him.

"Who the hell are you?" asked the inspector.

"I was about to ask the same thing myself. Rupert on holiday, is he? Lazy arse – it was only three episodes, you'd think he could have managed that."

The inspector glared at him. "Look, whoever you are, you're not needed here. This is a simple case of suicide."

"Of course it's not suicide! Can't you see – the man was in the middle of ordering himself a takeaway?"

Sherlock pointed to the telephone receiver, which was off the hook and lying beside Van Mann's body, with a colourful leaflet next to it, emblazoned with the legend "Mr Woo's £5 All-Inclusive All-You-Can-Eat Chinese Buffet"

"It's not a very likely scenario is it? He goes to all the effort of dialling the number, says 'I'll have the prawn toast and the crispy duck', they say 'And would you like plum sauce with that?' and he says, 'Actually, you know what? On second thoughts, cancel that. Fuck it all, I think I'll put a bullet through my brain instead.'? He'd at least have waited until the prawn toast got here. No-one can resist prawn toast."

The DI was stroking his chin thoughtfully. He had to concede that Sherlock might have a point. Prawn toast was pretty damn moreish.

He sighed. "I'd like to follow it up. I really would. But if I say this is a murder, it'll mean a lot more paperwork and it will adversely affect our government targets if we don't catch the bastard. Much easier to just put it down as suicide, eh?"

"I understand your difficulty," said Sherlock, putting on his sympathetic voice, "I really do. Tell you what, why don't you let me and John here help you out? We can ask around a bit, see if there's anything in it, while you go back to New Scotland Yard, put your feet up, make yourself a nice cup of tea and listen to Classic FM. After all, we've already walked all over your crime scene, trampling the crap out of vital forensic evidence and breaking every police procedure in the book. In for a penny, in for a pound, eh?"

"Well, when you put it like that…" said the DI, clearly weakening. "So, if you catch the murderer, we can record it as homicide and I can take all the credit, but if you run up against a brick wall, we leave it as suicide and it doesn't have to blot our serious crime statistics?"

"Deal!" said Sherlock, shaking on it, before snatching up the Mr Woo's leaflet and turning on his heel, John following behind like a well-trained puppy.

"Don't worry," Sherlock confided, when they were out of the DI's earshot. "I had my fingers crossed. No way am I going to give that arsehole the credit if we can prove this is murder!"

"So you think the takeaway flyer could be a lead, then?" asked John.

Sherlock looked at him. "The dragon tattoo, the pink graffiti on the portrait. These are all the hallmarks of the Pink Pansy."

"The Pink Pansy?" asked John, intrigued.

Sherlock nodded. "An ancient Chinese criminal network. A bit like the Black Lotus, except they co-ordinate their accessories and have better taste in scatter cushions."

"But what's that got to do with a takeaway on the Kilburn High Road?"

Sherlock gave him a long hard look. "Bit of a coincidence, wouldn't you say, that Van Mann was taken out by a Chinese gangster at exactly the same time as he was ordering a Chinese takeaway?"

John shrugged. "I suppose."

"I don't believe in coincidences. Let's check it out. Taxi!"

They arrived at Mr Woo's at a bad time. Evening service was in full swing and the manager really didn't want to talk to them. He was adamant, though, that no-one by the name of Wight Van Mann had ordered a takeaway that afternoon.

"Hmm," mused Sherlock. "So he ordered the prawn toast under an assumed name. I wonder why?"

They were just pondering this point, when John noticed a boy with bad acne staring intently at them from behind the naff beaded curtain that led into the kitchen. He was just wondering if the boy fancied Sherlock or if he was just taking advantage of an opportunity to skive off from the washing-up, when the spotty one winked at them and made a discreet beckoning gesture. Ah, so he did fancy Sherlock, then.

To John's astonishment, Sherlock got up, went over to the boy and disappeared behind the beaded curtain. Really! They were in the middle of a case! This was not a good moment to start cottaging with a pizza-faced adolescent in an area where food was prepared.

But a few seconds later, Sherlock's head appeared through the beaded curtain and he started beckoning John over, too.

"Psst!" he projected, in a dramatic stage whisper. "I know what you're thinking, but it's not like that! Credit me with some taste! The boy has information which could be relevant to our investigation!"

Intrigued, John, too, disappeared behind the beaded curtain, where Joey was anxious to tell the two investigators about something which had been worrying him all afternoon.

"There's this girl who works here. Yu-No Hoo. It was supposed to be her shift this afternoon. She came in, as normal, laid the tables, did all the serviettes, but just before we were due to let the punters in for lunch, she vanished off the face of the earth. I tried to talk to the manager about it, but he said she must have just had enough and done a runner. Happens a lot in catering, he said. It's the split shifts, you see. Gets to a lot of people in the end."

"But you think it was more than that?" probed Sherlock, gently.

"She hadn't been paid yet. If you were going to walk out of your job, you'd make sure you collected your wages first, wouldn't you? Plus she left her coat and bag behind," said Joey, holding up a puffa jacket and a handbag. "All her credit cards are still inside. Why would she have left them? And all the doors and windows were locked at the time she disappeared, so she must have crawled out of the ventilation shaft for the extractor fan. I can't put my finger on it, but something's just not quite right here."

Sherlock leant forward and stared very intently into Joey's eyes. "Do you remember a customer called Wight Van Mann eating here or ordering a takeaway?"

Joey shook his head.

"Ever heard anyone here mention the Pink Pansy?"

Joey shook his head again.

"And you haven't noticed anything else strange happening at Mr Woo's recently?"

Joey shook his head for the third time.

Sherlock straightened up. "Then I'm inclined to agree with your boss. Maybe the mingy tips were just doing her head in. Come on, John! I don't think there's anything useful for us here."

"Oh," remembered Joey, when they were halfway out the door. "There was one thing. A whole load of pink graffiti appeared in the staff toilet about the same time as Yu-No disappeared."

Sherlock and John caught each other's eye and rushed to the staff toilet cubicle.

As in the dentist's surgery, there were numbers scrawled in pink on the wall, but this time there were four numbers. 7, 3, 34, 15.

"It's a warning," murmured Sherlock.

"A warning?" echoed John. "What, you mean like one of those little yellow plastic signs they put up to tell you the floor's wet?"

"No, I mean like one of those little signals they send you to tell you they're about to slash you up, rip your intestines out with a teaspoon and knot them round your neck like a scarf! A death threat. In code. That's it!" exclaimed Sherlock. This is what this is all about! They murdered Wight Van Mann and now they're out to murder Yu-No Hoo!"

John looked at him blankly. "Er, no, sorry, I don't know who. You're being a bit too subtle for me there, mate."

"No! Not You-Know-Who, Yu-No Hoo!"

"I'm telling you, Sherlock, I don't know who you mean."

"YU-NO HOO! The bint who works here!"

"Well, why didn't you just say so in the first place?"

"Those numbers – they contain a hidden message. They must refer to something, some printed cipher that only the gang members are aware of." Sherlock turned to the spotty washing-up boy. "Joey, do you know Yu-No's address?"

"Of course I know her address!" said an indignant Joey, his professional pride dented. "I'm a fully paid up member of the National Union of Stalkers! I could also give you her phone number, the name of her first pet, a detailed log of all her movements over the last six months and some grainy footage of her changing, if you wanted?"

"Er, no, the address would do just fine, thanks."

While they were en route, Sherlock explained his deductions to his assistant. "She's obviously a member of the Pink Pansy who's broken loose. She's come to England to start a new life and put her criminal past behind her. But they've followed her here and found her."

John looked confused. "Hang on – the address Joey's given us, it's just off Shaftesbury Avenue?"

"Uh-huh," confirmed his flatmate.

"But, Sherlock, if she's in hiding from a Chinese gang, fearful of her past Chinese life catching up with her, desperate to avoid any contact with Chinese people who might pass on any hints as to her whereabouts to her former Chinese masters, then why has she rented a flat slap bang in the middle of Chinatown? It doesn't make any sense. I mean, not many Chinese people there, right?"

"Bugger me!" murmured Sherlock, in awe at his flatmate's razor-sharp insight. This subtle piece of deduction had never occurred to him. He flipped through his mental Filofax for a few seconds, searching for possible explanations, but, completely stumped, finally shrugged, "No, you've got me there, mate. Maybe she's just a bit thick?"

And, indeed, when they got to Yu-No Hoo's flat, it was immediately apparent that she wasn't the brightest bulb in the box.

"I'm not here!" she yelled out of the window when they rang the doorbell. And then covered her eyes with her hands in a piece of fiendishly cunning disguise.

But they managed to coax her into letting them into the flat by pretending they'd come to read the gas meter.

Once inside the door, Sherlock said, "I'm afraid I have a confession to make, Miss Hoo. We aren't really from the gas board."

Yu-No's face drained of all colour. "Oh, bollocks!" she said. "Please don't tell me you're from the Jehovah's Witnesses! I had them round last week, as well, and it was the devil's own job trying to get them to piss off once I'd let them over the threshold."

"No, no," Sherlock assured her, soothingly. "We are not from the Jehovah's Witnesses." He paused for dramatic emphasis. "Nor are we from the Pink Pansy."

"Oh!" she exclaimed, in shock. "So you know my secret?"

"What? Your sad little addiction to crap Australian soap operas? Or the fact that you woke up this morning without any clean knickers, so you just turned yesterday's pair inside out?"

She blushed. "Well, both of those, as well. But, er, actually, I was thinking about my secret criminal past as a smuggler of narcotics and fine antiques."

Sherlock and John stared at her, expectantly, waiting for her to spill the beans.

"I was young, very young," she said, finally. "My family, we were very poor. We no could afford enough food to eat. I have no choice. I have to join the Pink Pansy or I starve in street. I think it will just be for little while. Just until I save up enough money for latest model of I-Phone and high definition flat screen telly. But I get sucked in, deeper and deeper, and one day I realise they will never let me go. So I make plan. I run away and come to England. I tell myself that I am safe now, that they forget about me, that I can start new life. But, deep down, I always know that they no forget, that one day they follow me here and punish me for my treachery. And I am right. As soon as I see graffiti in staff toilet, I know that I am dead woman. I try to hide here, but I know it is no good. They will catch me and crush me like man stamping on beetle. Just thinking about it scare me so much, me forget the difference between past and present tense and resort to speaking silly kind of Pidgin English."

"There, there," murmured Sherlock. "You're safe now. We are here to protect you. Just help us to crack the code, then we'll catch the bastards and you can start speaking in normal grammatical sentences again."

"Ah! The code!" she said. "It's based on…."

But she never finished the sentence, as at that moment they heard a kind of scraping noise at one of the bedroom windows. Someone was trying to break into the flat!

Sherlock immediately pulled a revolver out of his pocket and headed for the front door.

"I'm going to check out the front. John! Whatever you do, stay here and look after Yu-No Hoo! Whatever happens, don't move from this room, OK?"

Nothing happened for about twenty minutes. John started to get very bored and was seriously contemplating asking Yu-No if she fancied watching a bit of daytime TV to pass the time. It would be grim and they might even have to cope with Alan Titchmarsh, but the circumstances were desperate.

Suddenly, a rapid burst of gunfire could be heard outside the flat. Sherlock could be in trouble!

John's military training enabled him to make a split-second assessment of which target he ought to prioritise when there were two who both needed his protection simultaneously. He ran through a checklist now. Yu-No was an unarmed, female civilian, about half the body weight of Sherlock, the known target of the criminals they were investigating, she had received a death threat less than 24 hours before and he had been directly ordered to stay and protect her. Balanced against this, Sherlock still owed him fifty quid and had a cuter bottom. There was no contest.

"You stay there, love," he said, patting Yu-No on the arm. "I'm just nipping out for a bit. Won't be long. Well, hopefully."

He tossed her his mobile 'phone.

"Tell you what, if a horde of murderous Chinese gangsters happen to break into the flat while I'm out, you could try ringing 999."

He was halfway to the door when he had a change of heart.

"Actually, on second thoughts, could you use the landline? I'm a bit low on credit."

He sprinted out of the front door, but Sherlock was nowhere to be seen, although it looked like someone had been taking potshots at the pavement.

He jogged round the block a few times, looking for his flatmate behind bins and in shop doorways and he was just beginning to think that maybe he ought to retrace his steps and start looking for Sherlock in places he knew he couldn't be, either because he'd already looked there or because they were totally mad places, like the top of the wardrobe or that gap that everybody always forgets about behind the fridge, when someone crept up behind him, slapped their hands over his eyes and yelled, "Guess who?" in an annoying sing-song voice.

"Sherlock, stop doing your Moriarty impersonation again, you scared the shit out of me! Found any gangsters?"

"Nope."

"But I thought I heard gunshots a while back?"

Sherlock blushed. "That was me. You know that thing where you accidentally sit on your 'phone and find you've left a long message of traffic noise on your own voicemail?"

John nodded. He'd done that a couple of times himself.

"I kind of did that. Only with my gun." He held up the back of his coat, which now resembled a colander. Then a thought occurred to him and his eyes narrowed. "I thought I told you to stay and look after Yu-No?"

"Relax, Sherlock! She's absolutely fine. When I left her she was as happy as…"

They heard a loud bang coming from the direction of Yu-No's flat.

They immediately ran back to the flat, hoping against hope that the noise they had heard was just a car backfiring, the washing-machine blowing up or the next door neighbours shooting each other up in a completely unrelated drugs turf war. But when they got there, Yu-No Hoo was lying on the floor, most of her chest blasted away by a gunshot fired at close range.

John took a sharp intake of breath. "Unlucky!" he said. "What were the chances of that happening, eh?"

He went in search of a landline to telephone for an ambulance to take the body away, but Sherlock noticed a faint movement in her face. She was not quite dead. And she was trying to move her mouth. With her dying breath, she was trying to say something.

He knelt beside her and whispered into her ear:

"What is it, Yu-No? Who did this to you? What are you trying to tell me?"

She pressed something into Sherlock's hand and, although it caused her great pain, she managed to force out the words, "They do a very nice Egg Fried Rice."

No sooner had she managed to finish the sentence, than she collapsed stone dead in Sherlock's arms.

He looked at the piece of paper she had been so anxious to give to him before she breathed her last. It was a menu from Mr Woo's £5 All-Inclusive All-You-Can-Eat Chinese Buffet. Well, there was dedication for you. While dying an unimaginably painful death from a gunshot wound, she still wanted to do her best to pimp the takeaway where she worked.

"She's got a point, though," mused John, when the paramedics had come and taken the body away. "We could take a break and go for noodles. All this running around has made me hungry and, seeing as we're in Chinatown, anyway…"

He started wistfully eying the restaurant across the street.

Sherlock walked across to it.

"You can always tell a really good Chinese by observing the bottom third of the door handle."

He leant down and scrutinised the handle through his powerful magnifying lens.

"Oh, bugger," he murmured. "This one's a bit shit. Never mind, we need to get out of the rain and I do my best thinking when I'm inhaling large clouds of monosodium glutamate."

He pushed open the door with his hip and they made their way to one of the formica tables at the back of the shop. John immediately started scanning the menu, but Sherlock was intent on business.

"We need to crack this code!" He exclaimed, with frustration. "It's obviously based on a piece of printed material which is widely available– a piece of printed material that contains numbers, lots of them. The answer must be staring me in the face. Now think, Sherlock, think!"

At this, he started slapping the side of his head, as if it were a dodgy slot machine that had just swallowed his last 50p without giving him any chocolate.

John, however, was barely listening. Eyes firmly fixed on the menu, he was more interested in stuffing his face.

"I'm starving! I think I'll have No. 2, the Crab Soup, followed by No. 14, the Prawn Chow Mein, then No. 32, the Banana Cake, all washed down by No. 64, the Shockingly Overpriced Imported Beer. What about you, Sherlock?"

Sherlock stared at him, irritably.

"John, you know very well that I never eat when I'm on a case. I'm just going to go for No. 56, the Tap Water…OOOOHHH!"

He dropped the menu and immediately contorted his face into a spectacular piece of gurning – sort of a cross between Frankie Howerd's signature expression and the face of the average person when they are in the middle of a particularly difficult and not inconsiderably painful dump. Some of the other diners were looking at him and wondering if it was such a good idea to proceed with their meals if that's what the food here did to you, but John knew by now that this usually just signified he might be coming up with an idea.

"That's it! John!" he panted, breathlessly. "The code! It's based on the menu at Mr Woo's £5 All-Inclusive All-You-Can-Eat Chinese Buffet!"

"Hang on a minute," said John, baffled. "A buffet doesn't need a menu. That's kind of the point – you serve yourself."

"Exactly! The clue's been in front of us all this time."

"Ah," exclaimed John, the scales falling from his eyes. "So THAT's what Yu-No Hoo was trying to tell us before she died!"

They simultaneously scrabbled around in their bags to find the menu they had found at Van Mann's flat and the one which the dying woman had pressed on them just before she conked out. They took a menu each and busily applied themselves to decoding the cipher.

Soon they each had the same words scrawled on a napkin:

7 = Dim Sum

3 = Bird's Nest Soup

34= Your Choice of Dessert (See Trolley For Today's Selection)

15= Fried Rice

"Oooh, look!" squealed John, at last. "It's only the first word of each menu item that counts! It was a death threat to Yu-No Hoo! 'DIM BIRD, YOUR FRIED."

Sherlock shook his head, sadly. "Terrible. They can't even tell the difference between 'your' and 'you're' and yet they're running a global criminal empire worth billions of pounds, while we're living over a dodgy sandwich shop off the Euston Road. I tell you, we're in the wrong job, John."

"So what do we do now, Sherlock?"

"Do?" asked Sherlock, raising an eyebrow quizzically.

"Yeah, " said John, with the eagerness of a boisterous young Golden Retriever dying to be let off the leash. "We've cracked the code. So, now, how do we go about tracking down the criminals?"

"Oh, we don't need to bother doing that," said Sherlock, nonchalantly. "I normally just wait for them to turn up at my flat for no discernible reason, helpfully alert me to their identity of their own accord and then abduct any random person who happens to be on the premises at the time. That's how it usually works. Damned nice of them – saves me a hell of a lot of hassle actually having to try to work out who they are.

Hmm. Actually, you know, that soup does look rather nice. Mind if I share?"