T for little bit of language, little bit of violence, and a lot of fake blood.

No spoilers, except for series 1.

Happy Halloween!

Halloween has sort of become like April Fool's Day in the Holmes and Watson household. It's more Sherlock's style – he gets an excuse to leave even more severed body parts lying around than usual – and it's always entertaining for John to watch Sherlock squealing in horror as a bucket of fake blood drenches him the one time he actually returned with milk after leaving to get it. Safe to say, that hasn't happened since.

However, this year, their Halloween antics have seeped out of the confines of the flat and infiltrated – uh – other areas of their lives too.

When Lestrade rings them up on the morning of the 31st of October with news of a brutal murder among the ruins of a dilapidated old castle, the excitement emanating from one Sherlock Holmes is palpable. In fact, the setting is so perfect to what they've got planned, part of John fleetingly wonders if the world's only consulting detective has finally decided to dip his toes into crime…but Sherlock's radiation of pure glee, the way his tongue darts out to moisten his lower lip in anticipation, as well as a wide grin spreading across his features, all seem to suggest not.

He's just as delighted as John is as they throw various gruesome items into a rucksack, and Sherlock calls Lestrade back.

"Have you got a car?"

There's a bewildered pause.

"A car?" the Detective Inspector repeats. John thinks he sounds a bit stunned.

"Yes, a car," Sherlock reiterates, rolling his eyes, and sighing. "A police car…to get to this supposedly terrifying castle. The cab fare is likely to be astronomical."

He hangs up, smirks at John, and ten minutes later a rather bemused Lestrade appears beneath their window in his police car, the blue lights for once still and dark. Sherlock seizes his coat, pushes John in the direction of the stairs, and they meet Lestrade outside with his hand poised in mid-air, about to knock.

"Come on then," Sherlock instructs, sweeping straight past him without greeting, and wrenching open the back door of the car. He disappears inside, and John and Lestrade walk over slightly more sedately, exchanging friendly 'good morning's as they go.

Sherlock spends the first fifteen minutes of the trip as usual; extracting as much information as he can get about the case out of Lestrade: the setting, the victim, any fingerprints, have they run the credit cards yet, and, Lestrade, why on earth would we assume this case is connected to that murder three months ago at Oxburgh Hall? That is the kind of assumption a five year old high on blue smarties would come to. A five year old orang-utan.

Once he's finished demolishing everyone else's ideas, Sherlock dissolves into quiet muttering and furious tapping on his phone. John catches phrases like 'Birmingham, possibly…no, obvious, the aunt' and 'manslaughter? Possibly too messy…need more data' but his mumblings are to John as indecipherable as ever, and he spends the best part of an hour staring at the back of Lestrade's head, and hoping that Sherlock hasn't forgotten their plan, because otherwise he could have actually been earning some money.

Sherlock does eventually stow his phone in his coat as ruins crawl into view through the mist – oh, all very atmospheric – and the sidelong grin he shoots at John confirm that he has most definitely not forgotten their plan.

The car slows to a stop on dewy grass, Lestrade swings his legs from the car, and Sherlock moves.

He aims a heavy punch at John's left shoulder that just falls short. John swears in pain as best he can, and he feels the cold dampness of Sherlock's hand under the collar of his jumper.

Lestrade has noticed their scuffle, and instead of just leaving them to follow him towards the crime scene, he turns back towards the car he's just exited, and pulls open the door next to John's seat. Something heavy falls to the floor.

"Sherlock!" John cries, annoyance lacing his voice. He clutches at his injured shoulder and gasps, feeling the dampness ooze between his fingers. "What in hell do you think you're doing?"

It's at this point Lestrade's face appears through the car door.

Sherlock is shaking slightly, eyes fixed on John's shoulder, apparently at a loss for what to say. John sits very still, looking rather shell-shocked. One arm of his jumper hangs loosely by his side, his left shoulder is seeping red through the wool, and a severed arm lies, useless, on the floor of Lestrade's car.

Lestrade himself seems to be reeling – anger, shock, concern – they all flit through his eyes, which are almost bulging out of his skull. His hand twitches by his side, as if about to reach for a phone.

The illusion only lasts for a second: a bark of laughter rips from Sherlock's lips, utterly uncontrollable. Seconds later, he and John are both doubled over, almost howling with mirth, unable to do anything but clutch at each other and desperately gasp for air.

Eventually they do get out of the car, and are allowed to see the body, under the condition that they never, ever do anything like that again. Sherlock nods impatiently, bouncing on the balls of his feet and craning his neck to see over the police line.

Only John sees the fingers crossed behind his back.

Case solved – more or less – Anderson's team in (presumably as an experiment to see how much evidence it's possible to miss), and Sherlock and John are free to go. They take the opportunity to roam the ruins of the castle as opposed to going home, and to find a suitable location for their next trick. Sherlock selects the spot - secluded, a tumbledown room at the furthest corner of the castle - and the two set to work. Only the tallest point of a crumbling wall will be visible to anyone at a distance in this weather.

This stunt they can take a little more time over. Sherlock lays himself down on the cracked flooring, positioning his long limbs in such a way as seems appropriate to him. Meanwhile, John fishes their large bottle of fake blood from the bag, and sets about decorating his flatmate.

As Sherlock fidgets and grumbles, John daubs red liberally across his face, deliberately catching his hair, where it sticks clumps of inky curls together with congealed stickiness. Sherlock squirms. John continues splashing red from his mouth and nostrils, and creates gaping cuts across his cheeks and forehead.

"I'm supposed to be injured, John," Sherlock complains, as the doctor continues to create various hideous and bloody injuries across his face "Not have had an unfortunate run in with a bucket of red paint."

John leaves the face ('shame') and goes to douse the floor with red, as if Sherlock had been bleeding over the rock. At this, the detective sits bolt upright and glares.

"What?"

"My coat!" Sherlock wails. Obediently, John waits for him to shed it, rolls it up and stows it in his bag. He then pushes his friend back down to the ground, and carefully pours blood all around his torso.

"Hey!" John yells, running as fast as he can towards the dark shapes that he knows are Anderson and Sally Donovan on a tea break. He skids to a stop on the wet grass, and tries to catch his breath. They both stare.

"There's – something over there," he gasps, pointing in the direction of his concealed flatmate. "Sherlock…he said he saw something. Moving."

John nods, takes a breath, and runs straight back into the gloom.

Behind him, he hears the pair grumbling, but muted footsteps confirm that they have followed him. His eyes scan the whiteness for that peak of the wall bordering Sherlock's hiding place.

"Over here!" he calls, wading further through the mist to where he knows Sherlock lies. When his grinning, bloodied face swims into his line of vision, John walks straight over him, hides behind one of the more intact walls, and waits for the two police to catch him up.

There is a horrible, piercing scream, followed by manic cackling.

"THIS IS A CRIME SCENE," Anderson bellows at them, pulling at the lapels of his coat and trying to compose himself. John pops his head around the stone, and flashes a smile at Sherlock. Anderson is grinding his teeth; Sally sighing and rolling her eyes, and Sherlock positively beaming. "For the last time: I DON'T WANT IT CONTAMINATED."

Sherlock stretches back in the restaurant chair, and yawns. He reminds John of a cat – all elegant disdain, even when he's tired.

"That was fun," the detective comments lightly, sipping his coffee. The waitress comes over, and Sherlock delves into the bag to find change. "Hang on."

He starts to empty the bag onto the table. When he gets to the severed arm, the girl shrieks and jumps away from him.

Sherlock's smiling apologies aren't particularly sincere, John thinks, and stowing the arm back in the bag understandably isn't quite enough for the terrified waitress; she disappears into the kitchen to fetch her manager.

Catching his breath around the nearest corner, John reflects that he can't remember the last time he got to finish a meal where Sherlock Holmes was involved.

They're out of milk again, and John steers Sherlock into Tesco on the way home, before he forgets.

He is just walking over to the chilled section, sulky detective in tow, when suddenly hands grab his shoulders and swing him round. He gets a glimpse of Sherlock's face, a face that seems to be getting unacceptably close to his own far too fast…and he's just flailing around in his brain, trying to compute what the hell's about to happen, when he feels a sharp pain in his neck, and Sherlock's warmth vanishes.

John realises he must have let out some exclamation of pain, because people are looking – no, staring – at them, mouths agape in horror.

The next thing he realises is that his flatmate has just bitten him. Hard. On the neck.

In a fucking supermarket.

John looks at him.

Sherlock's got fake blood pouring from his mouth over his pale skin, a wolfish grin igniting his eyes.

They get kicked out of there, too.

They run gasping with laughter up the stairs to their flat, and flop down into the sofa simultaneously.

"That. Was amazing," John states, giggling. He wipes the blood from his neck and smears it slowly and deliberately down Sherlock's cheek with his whole hand. "I'm surprised we weren't arrested."

"Me too," Sherlock agrees, a chuckle rising in his throat to join John's. He's still slightly breathless, and grins again.

"Although – " John goes on. "If you ever bite me again..."

Sherlock's smile widens, and he leaps from the sofa, whirling to face his flatmate. He looks manic and excited, and his mouth is still far too red from all the fake blood. He looks practically feral.

"One more thing," he says. He holds up his forefinger, and briefly disappears into the bathroom to wash off all the accumulated blood. John hears him gulp water, and spit into the sink, followed by a good deal of splashing. He reappears about thirty seconds later. His hair is damp, and he's holding his ruined shirt balled up in his fist. "Mycroft."

Sherlock dials the number carefully, and presses his phone to his ear. His bottom lip juts out slightly, resenting the need to use his brother's preferred method of communication. John notices, and sniggers.

"Hello Sherlock."

The detective sniffs.

"Good evening."

"What can I do for you?"

There's a pause, in which Sherlock pretends to be sulkily contemplating his answer, but which he actually uses to throw the severed arm at his flatmate, who is still laughing at him.

"It's John," Sherlock says. He sniffs, and touches the tips of his fingers to his mouth. "He is behaving rather…strangely."

This isn't a total lie: John is now doubled over in silent stitches, hand over his mouth, trying not to make any noise.

"Nothing you can't handle, I'm sure."

"Why?"

"Fine." There's a silence. "I'll send Anthea."

Sherlock says nothing, but the set of his lips morphs into a frown. Apparently, this is detectable over the phone.

"Naturally. I'll be along."

The line goes dead. Sherlock looks at John.

"That was friendly," John comments.

"I couldn't act differently to normal; it would have been too suspicious," Sherlock snaps. His frown switches instantly to a smile. "Come on."

The next 20 minutes is spent absolutely tearing the place apart. It's like a very odd sort of interrupted play, John thinks, as he daubs Chinese symbols on the wooden flooring with the fake blood – deadman, from the Blind Banker case – with Sherlock peering around the door of his bedroom, arms flailing as he tries not to move his feet.

"Could you at least try and hurry?" Sherlock asks irritably, swaying dangerously. "It won't take Mycroft more than half an hour to get here."

"Yes, alright," John snarls, scrawling a bit more aggressively.

Once he's finished drawing on the floor, Sherlock sweeps dramatically into the room. He halts very suddenly, the rug beneath his feet rucking as he almost skids to a stop.

"John," he breathes, and the doctor is reminded forcibly of his expression when he had stepped out of that cubicle at the pool, and Sherlock had set eyes on him.

"Yes?" he asks, slightly confused. He furrows his brow, and Sherlock throws his hands up in apparent despair.

"Could you at least try and play along?"

John laughs.

"I thought we were setting up a practical joke for your brother, not starting our own theatre company."

"Yes," Sherlock explains, his exasperation clear in every syllable. "But this is Mycroft, John! He'll notice if we just throw the furniture around a bit."

John complies to a degree, although he refuses flat out to participate in Sherlock's theatrics: he does as he's told, trips and jumps and runs as instructed…but he draws the line at dramatic dialogue. Mycroft couldn't tell what they'd been talking about.

He ties Sherlock to a chair, he climbs out of the bloody window, he even fires a missed shot past Sherlock's ear as the detective artfully splashes blood on the wall. Sherlock won't allow him back into the house once he's out, in case Mycroft notices foot marks that couldn't have been made previously. John thinks Sherlock's probably going a bit far when he makes him recreate the swimming pool on the kitchen floor, although Sherlock assures him he waterproofed the whole floor a long time ago in case of emergency, so Mrs Hudson wouldn't get wet. John doesn't like to ask what kind of emergency he was anticipating, living on the first floor.

He stands outside the window in the cold, and hears Sherlock crashing around inside. As he falls silent, John hopes that his laptop has escaped Sherlock's destruction. The detective's voice calls to him out of the open window.

"John?"

"Sherlock?"

"Text me: 'the art of disguise is knowing how to hide in plain sight, Mr Holmes. But don't look like that. Practically everyone's an idiot. "

"The art of what?"

"Oh, for f – "

It takes about a minute for Sherlock to dictate the message, and John to tap it in and hit send.

"Trust you to want such a sodding wordy text."

"John, hide! It's been almost half an hour."

John does as instructed, ducking into the nearest alleyway, hoping the darkness will be enough to conceal him from Mycroft. He can still see the light from Baker Street, and keeps his eyes fixed on the window.

A few minutes pass, and Sherlock joins him in the darkness. John's only alerted to his presence when his hand grabs his shoulder and pushes him further into the blackness. His clothes are damp from the 'pool'.

"Sherlock, are you sure he's coming?"

The question is met with stony silence; John takes that as a condescending 'obviously'. They exchange glances, smile, and scuffle to get the best view of the flat.

Mycroft arrives not long after, in his usual conspicuous vehicle. Despite the fact that they're supposed to be being quiet, Sherlock lets out a very audible scoff.

As he disappears inside, time seems to lose all meaning - John's not sure if he's been in there just a few seconds, or much longer. Everything seems the same in the dark.

Sherlock doesn't seem to have this problem: he gives Mycroft 'about a minute' to investigate the flat alone, and then the detective moves…half running, half staggering across the street, clutching his bloodied side. John watches as he crashes in through the front door, and waits, a wide grin spreading across his face.

Something hard slams into John's head, and he grunts in pain, instinctively lashing out at his attacker. His fist connects hard with the other man's jaw. It crunches against his knuckles, but the man, whoever he is, already has a tight grip on him. Fabric is pulled over his head, his hands are jammed behind his back. He struggles for all he's worth, pulse hammering in his throat. He tries to yell out, but wool has been shoved tightly into his mouth and he can't. He kicks out, trying to find his captor's groin, but the more he squirms and kicks, the tighter the man's grip holds.

"Gotcha, Mr Moriarty," an unfamiliar voice in his ear snarls, and John realises far too late that this joke has backfired severely. He needs Sherlock to come back outside, but he's still with Mycroft, and John knows he'll try and suspend Mycroft's disbelief as long as he can – and meanwhile, John is being shoved into a car, blind.

"Sherlock!" he tries to yell, but it's just a muted and unintelligible grunt. He fights to spit the wool out. The car's engine has started and he has to struggle to stop panic setting in. The wool snags on his teeth, reluctant to leave his mouth. He keeps at it, jabbing at it fiercely with his tongue, until it finally rolls out onto his chin.

"SHERLOCK!" he bellows, praying the window is open, and that this is 'just' the police, and not one of Moriarty's enemies. "Sherlock, the car!"

He hears the front door reopen, and then Sherlock's answering cry, although he's not sure what he says. The car door is wrenched open just as he feels it start to move, and the next thing John sees is Sherlock's stricken face inches from his, the detective's fingers fisted around the bag that he's just snatched from John's face. He hauls John from the car by the front of his jumper, panting hard.

"John," he says, relief evident in his heavy breathing and the startled look in his eyes. He drags him further from the car, which ominously is just an ordinary Golf, and it's stopped. Sherlock frowns, eyes flicking over John's face. "Are you…?"

"Fine. I'm fine. He said…he thinks I'm Moriarty…I think this backfired a bit."

Sherlock smiles at the understatement, his attention now fixed on the man stalking round the car towards them. John steps forward stolidly, clenching his jaw in preparation. He can feel the detective bracing himself too.

However, before he reaches them, another person emerges from the Golf. John hears Sherlock's breath hiss between his teeth, and a strangled 'No!' escape from him.

This second man strides into the headlights of Mycroft's car, and John's jaw drops open too.

Detective Inspector Lestrade almost strolls towards them, grinning broadly. He walks straight over and shakes first Mycroft's hand, and then the hand of the man that John doesn't know. All three smile just as widely as Lestrade.

Sherlock can do little except splutter, and John just shakes his head, and concedes to himself that they deserved that. His heart is still hammering wildly in his chest though.

Sherlock, on the other hand, is far less gracious.

"That – that's cheating!" he cries, glaring at his elder brother. He gives a contemptuous huff at the gathered men and storms off, slamming the front door behind him.

John goes to follow him, but the piercing scream as he reaches for the door handle causes him to step back.

There's an ominous silence. Then:

"JOHN! HELP! THERE'S A TARANTULA! IN MY HAIR."