A/N: I started writing this just after series three finished (nearly three years ago, argh!) and have only just gotten round to finishing it. It's set somewhere between episodes one and two of series three, and is based on a throwaway line from episode three. Enjoy!

Thirty Thousand Teeth

by Flaignhan

Her eyelids flutter open at the creak of a door hinge. She sits bolt upright, her heart thudding in her chest, her hand fumbling for the lamp on her bedside cabinet. Her fingers manage to catch the switch, and after a moment, she is blinded by light, her eyes squeezing shut instinctively, before she forces them open, to find the source of the noise.

"Get dressed," he says, his voice immediately settling her. All panicked thoughts of murderers and burglars slip from her mind as her eyes focus on his coat collar, still turned up from shielding the back of his neck from the rain outside, which patters against the window. She blinks, her brain taking a while to kick in, and she turns to look at her alarm clock, her eyebrows drawing into a frown when she sees that it's a quarter past two in the morning.

"Hurry up," he says, and he grabs the nearest pair of trousers - cast onto the chair in front of her dressing table as a result of late night laziness - then tosses them to her.

"What's happened?" she yawns, pushing her duvet off of her and shivering as the cool air hits her, goosebumps raising on her skin. She looks down at the cotton trousers Sherlock has picked out for her and she decides against them, figuring that if she's going to be dragged out in the middle of the night, she might as well be warm.

She stands, and stumbles over to the wardrobe, pushing Sherlock gently out of her way with an uncoordinated movement. She opens the doors, peering into the selection of clothes on offer, then pulls out a cosy looking woollen dress, with long sleeves that she knows will fall well past her wrists, allowing her to tuck her fingers away from the cold.

"We're going on a trip," he tells her, taking a step away from her chest of drawers as she approaches. He doesn't leave the bedroom however, apparently unconcerned about the fact that she might want some privacy while she changes. She rifles through the topmost drawer until she finds a pair of thick knitted tights.

"Where to?" she asks, glancing up at him before she chucks her clothes onto the bed. She moves past him, out into the lounge , and flicks on the light.

"Let's call it a surprise," he says, following her out of the bedroom, his hands clasped behind his back, a smug smile curving his lips. Molly rolls her eyes and continues towards the bathroom, where thankfully he allows her an ounce of peace. She brushes her teeth, and outside hears the sound of the kettle boiling. It's as though a warm light has ignited in the pit of her stomach, promising her of some sort of salvation when she leaves the bathroom. She has a quick wash, skips over her usual daily touches of make up (there's no point in hiding the dark circles under her eyes from Sherlock), then ventures back into the lounge. She hears Sherlock stirring sugar into a couple of mugs of coffee, and while he's busy, she disappears into the bedroom, getting changed as quickly as her tired limbs will allow her to. She triple checks that she's putting her tights on the right way before she begins the palaver of pulling them up, and she spends a good minute and a half straightening them out once she has them on. Happily, the soft wool immediately warms her legs, and the the burgundy dress is snug enough at the top to keep her toasty, but loose enough at the skirt to remain casual. She jams her feet into her tan brogues, then resolves to re-lace them, uncertain as to whether this trip that Sherlock has in mind will require any running or not. With that thought, she takes a hairband from her dressing table and pulls her hair into a loose knot; practical with minimal effort. Just the way 2AM adventures ought to be.

When she heads out into the lounge once more, a steaming mug of coffee is pushed into her hand, and she takes a testing sip, noting that Sherlock has topped it up with cold water to make it more suitable for drinking quickly. It's still a touch too hot, however, and so Molly puts it down and goes to put on her coat, while Sherlock, with a mouth that is apparently made of asbestos, sips at his own coffee, his eyes watching her every move, as though trying to calculate exactly what her next step will be.

"Is there any reason this trip has to be at this time of night?" she asks, barely suppressing a yawn as she buttons up her coat.

At this, he smiles that irritatingly smug smile again, and Molly knows she won't be receiving any sort of straightforward answer.

"You'll see," he says quietly. "Drink up."

She follows his instructions, and drains as much of the coffee as she can in one go, abandoning the rest in favour of haste. Sherlock doesn't say a word as he strides towards the door, just pulls it open and waits for Molly to exit before he closes it behind them.

"Are you going to give me any clues at all?" Molly asks, as Sherlock presses the button for the lift, his fingers jabbing it impatiently.

"No," he says plainly, his eyes narrowed at the LED display next to the lift doors, displaying the changing floor numbers as it trundles slowly towards the fourteenth storey.

"Why?" Molly asks, just as bluntly. If he's dragging her out of her flat in the small hours, then she thinks she deserves some sort of explanation, excitable butterflies in the pit of her stomach be damned. She's got a long shift tomorrow, with three examinations already scheduled in, not including the victims of tonight's scattered mishaps to contend with. There will, inevitably, be a fall in some old dear's house, a drug overdose in some grotty pub toilet, or a fight that gets out of hand. She wishes people would just go to bed early some nights, give her a chance to catch up, to send one body off to the undertaker with all its paperwork filed and sorted, and not have to turn around and deal with a new one straight away.

Still, it is of some, morbid comfort that she acknowledges that she'll never go out of business. She won't have to retrain when she hits her forties because there's a supply and demand issue in her industry.

"Just wait and see," he says. "It's for a case, but it'll be worth it."

She narrows her eyes, but at that moment, the lift arrives, the doors opening with a soft ding, and they step inside, Sherlock tapping the button for the ground floor. Molly slides her hands into her coat pockets, burying the bottom part of her face behind the collar of her coat, dreading the moment when they step out into the chilly, rainy night.

Thankfully, Sherlock hails a cab while she waits in the small recess at the entrance of her tower block. It doesn't provide much shelter, with the wind seeing to it that the rain attacks from all sides. The cab is nice and warm however, and the soft sounds of the late night program on Radio 2 almost lull her back to sleep. She rests her head against the rain spattered window, streetlights on the other side of the glass blurred by speed and poor weather.

They stop at Charing Cross, and Sherlock thrusts a twenty pound note through the small hole in the perspex screen, telling the driver to keep the change before he chivvies Molly out of the taxi. She shivers immediately upon her exit, and pulls her hood up, before looking around for any clue as to their destination.

Sherlock takes her by the hand and pulls her along, walking quickly, as though the wind isn't affecting his speed or balance at all. Molly gets pushed this way and that by particularly strong gusts, but she's not too worried. Worst case scenario, if she's going down, she's taking Sherlock with her, and the idea is almost too good to refuse. Were it not for the fact that the puddles are deep, dirty and completely uninviting, she would feign a stumble just to see him go arse over head once in his life.

She did see him jump off a building once, but she's not sure that really counts.

"Is John on a date night?" she asks, raising her voice so she can be heard over the rain. "Is that what this is?"

"No idea," Sherlock tells her, pulling her sharply to the right and down a narrow street lined with shuttered caf├ęs and bars. They walk quickly down the steep slope, and when they pass through the tube station at the end, Molly takes extra care not to slide on the slippery floor, littered with hundreds of wet footprints. Sherlock drags her up the steps of the Hungerford Bridge, and they walk at double speed, desperate to cross it before they get saturated. There is no protection up on the bridge, and they take the full battering of the unforgiving weather. With each step, Molly regrets more and more her decision to join Sherlock this evening.

She should have taken one look at the weather and told him to shove it.

"Why couldn't we get the cab driver to take us to the other side of the river?" she asks, quickly grabbing onto her hood as the wind catches it. She waylays the attempt to remove it from her head, but she keeps a firm grip on it, to avoid getting a faceful of rain.

The word he mumbles in response is lost in the rain, but from the movement of his lips, Molly is certain that it was witnesses. Her stomach turns over at this news, and she's not sure she's prepared to accompany him on any sort of illicit investigation, no matter how much the end result may justify it. She lets out a sigh, and allows him to guide her towards the steps that lead down to the Southbank.

She is forced to keep up with his rapid descent of the stairs, while he is apparently immune to any of those horrible little slips and slides that fill the heart with ice cold fear.

She makes it down in one piece, and he drags her off in the direction of the London Eye. Initially she thinks that they're heading up there, presumably up to the top to get a good view of some crime scene that he couldn't get when the place was full of tourists earlier on in the day. She's wrong, however, because he walks straight past it without a single glance upwards, no regard for the twinkling blue lights, nor the banners either side of it advertising river boat trips.

He leads her along, and Molly shrinks closer to him to try and protect herself a little more from the weather. He doesn't seem to care - his hair is saturated, locks sticking to his forehead, his scarf sporting large dark patches where it has absorbed the rain. It's only a few more minutes before they arrive at the front of a curved building that she recognises from her day to day passings. She looks up at the sign overhead, double-checking, because it seems so bizarre that he should drag her here, of all places, on a rainy, windy night. But here they are, at the London Aquarium, Sherlock fishing through his pockets and pulling out lanyards, fobs, and a large set of jangling keys.

"What are we doing?" Molly hisses, moving closer to him so he can hear. She is ninety percent certain that their presence here isn't remotely lawful, especially when she takes into account the picture of the balding man with brown eyes on the ID card in Sherlock's hand. He shushes her, and she folds her arms, casting her eyes around in case there are any other lunatics out on the Southbank on this god awful night. There is no one, however, and after a clattering of keys, the bleep of a card reader, and a loud, metallic click, the door opens.

Sherlock steps inside first, looking around, before gesturing for Molly to come in with him. She hesitates, then decides that there is probably some method to the madness, and even if the madness does land them in custody, Greg can probably sort things out. At least for her.

He closes the door softly behind them and locks it again, his movements careful, his ears obviously tuned to pick up even the faintest disturbance.

"Are you going to explain?" Molly whispers, goosebumps erupting over her skin as her eyes take in the dark, empty space.

"You heard about the kidnapped Cuban crocodile?" Sherlock asks quietly, before he runs his fingers through his hair and gives it a shake, getting rid of the excess water.

"Yeah it was in the Standard," Molly replies with a frown. "Are you investigating?"

"One of the directors claims that security is so tight here that it could only have been an inside job," he tells her, wiping his damp hands on his coat before he guides her through reception, bypassing the turnstile and opting for the exit gate instead.

"And this is all to prove them wrong?" Molly replies. "You broke into the London Aquarium to prove a point?"

"It's not quite as simple as that," he tells her, taking a cautious look into the corridor ahead before he deems it safe and heads towards it.

"But if security's so tight, why hasn't the alarm gone off?" Molly asks.

"Because they've got a security guard wandering around," Sherlock tells her. "You can't simultaneously have the alarm set and a guard inside. It wouldn't work."

"But isn't the alarm better? Because we've just gotten in with no trouble."

"I wouldn't say no trouble," Sherlock murmurs. "I had to follow the other guard to Ealing before I got a decent chance to pickpocket him. And even then I only got the lanyard and not the keys. Had to go in for a second attempt in a queue at Sainsbury's."

Molly shakes her head exasperatedly. "He's probably stressing out about it." She swats him on the arm, but he merely he raises an eyebrow.

"If he were that concerned, he'd have reported them missing, given recent events. If he's stressing, it's about his job, and not the welfare of the animals, nor the aquarium - "

"Maybe he's worried he'll be implicated in the previous theft if he tells them," Molly reasons, naturally inclined to give Sherlock's victim the benefit of the doubt.

"Maybe he should be implicated," Sherlock argues. He pushes open the door at the end of the corridor and they enter a room full of large tanks, the small, bright lights inside reflected by the water, giving the plain walls a tranquil, flowing texture. Sherlock peers into one of the tanks, watching a collection of tropical fish shimmy their way around the inside of the tank, but his fascination doesn't last long, and he's soon moving onto the next one, containing a handful of starfish, clinging to the rocks scattered around the bottom of their tank.

Molly moves on to the seahorses, and watches as they bob around, their dark beady eyes glinting in the tank light. Sherlock appears on the other side of it, his eyes meeting hers through the water.

She looks up when she hears the whistle, and in the room beyond she sees the swinging beam of torchlight, darting around the walls as though the torch itself is being waved casually around by its owner.

Sherlock darts around the tank, grabs her, and pulls her into a recess between two tanks. He drags her down, him resting on his haunches and leaning his back against the wall for balance, her practically sitting in his lap, her hands resting on his knees to steady herself. Her heart is beating wildly in her chest, her breaths coming short and sharp.

Sherlock places his hand over her mouth, forcing her to consider her breathing, to slow down, and to dispense with the racket her lungs had been making. As she settles, his grip loosens, though he keeps his hand in position, his spare arm looped around her middle holding her fast to him. Presumably he thinks she will be prone to toppling over and causing some sort of catastrophic incident that will not only give them away, but also destroy hundreds of rare and endangered fish in the process.

The warmth of his body is starting to fight off the dampness left behind by the rain, and she can feel his breath on the back of her neck; soft, calm, and apparently very used to this sort of thing. Guilt wrenches her stomach when she looks down and sees the sparkle of her engagement ring, and she balls her hand into a gentle fist, pushing thoughts of comfort, closeness, and, for the moment, Tom, out of her mind.

Her heart starts to pound harder when the security guard enters the room, his thick soled shoes slapping on the floor with each heavy step he takes. He continues whistling, an old Carpenters' song that Molly can't quite remember the name of, and the hand holding his torch swings back and forth like a pendulum while he walks, the beam bouncing around the walls. He's less of a deterrent to intruders and more of an invitation. He comes with his own alarm system, so you'd have to be on a similar level to the Home Alone bandits to be caught red handed by him.

He passes through, and Sherlock tugs Molly a few inches closer when the torch beam swings dangerously close to them. She's not entirely sure how she's managed to fit in such a small space with him, but she stays as still as she can, her fingers curving around the revere of his coat. She can feel his heartbeat through the material of his shirt; it's slow, and steady, and it calms her.

He's not worried.

The security guard disappears into the next room, but Sherlock's grip tightens around her waist, holding her in place until the sound of the footsteps have faded completely.

Molly stands up, reaching out a hand to steady herself against the wall, and Sherlock rises silently. She's grateful for the darkness; she can feel a blush rising in her cheeks, but thankfully the cool glow of the tanks isn't enough to give her away.

Sherlock edges around her, then leads the way into the next room. They bypass the stingrays and head for the tunnel up ahead.

As soon as they step over the threshold, they are bathed in shimmering light, the reflections from the water flickering across their skin. Molly glances up at Sherlock, the sharp angles of his cheekbones thrown into relief by the iridescent glow of the tunnel.

A shadow passes over them, and Molly tilts her head back to see a crescent shaped mouth brimming with sharp, pointed teeth. The pale body glides past the glass, and Molly touches Sherlock on the arm, his eyes following her gaze.

"Sand Tiger Shark," he murmurs.

They watch as it disappears into the blue, and after a moment, Sherlock gently guides her onwards, deeper into the tunnel. It's not long before they stop again, Sherlock's eyes fixed on another shark, watching as it cuts through the water with barely a ripple of disturbance.

Molly finds the information plaque, her eyes scanning over the words, drinking in the facts.

"They're older than trees," she says, looking across to Sherlock.

"Hmm?" He turns to look at her, his hands clasped behind his back. She's distracted him, but he doesn't seem to mind.

"Sharks. They're older than trees. Did you know that?"

Sherlock looks back towards the tank, and points to one of the sharks, drifting through the water. "That one doesn't look a day over twelve."

Molly suppresses a giggle and goes to join him, her eyes trailing the smaller, colourful fish wiggling their way through the water. Sherlock is fixated on the sharks, his gaze set every time one of them comes into view. He doesn't move a muscle, doesn't blink, though his breathing results in a faint mist on the curved surface of the glass.

"You all right?" Molly asks. She gives him a nudge with her shoulder, and he inhales deeply, as if surfacing from the depths.

"Don't you find them a bit..."

"A bit what?"

"Sinister?" he says with a grimace. His eyes flicker across to her, but then refocus on the movements of the closest shark - a Nurse Shark, according to the plaque.

"No," Molly says. "They might look a bit mean but that doesn't mean that they're not...good eggs."

"Good eggs?" he repeats incredulously. He turns away from the tank, presumably so he can focus all of his attention on mocking her. "Good eggs?"

Molly shushes him, her eyes darting towards the end of the tunnel for any sign of the security guard.

"Just how many sharks have you met which would qualify as good eggs?"

The temptation to utter the word 'you' is overwhelming, but she's not sure an argument would help their current situation. He probably considers himself to be a cut above most sharks.

"I just think you're making a sweeping generalisation," she tells him, maintaining a reasoned tone. "Why don't you like them?"

He settles down, his shoulders sagging, and he scans the tank again, just as one of the Sand Tiger Sharks eases its way around the rocks, its eyes glinting in the tank light.

"I don't know," he says. "They just...they look like they could destroy you, but they wouldn't bat an eyelid while doing it."

Molly frowns. "Do they even have eyelids?"

She is graced with a withering look, and then Sherlock pulls his phone out of his pocket, his thumbs tapping the keys rapidly while he does a search.

"Yes they do," he says triumphantly, but then his smile fades, and he adds in a mumble, "But they don't use them."

Molly beams, and turns her attention back to the fish. "Plus, Sand Tiger Sharks are very docile, and they eat small fish. So they're about as likely to destroy you as they are to bat an eyelid." She's pushing her luck now, but it's not often she gets to one up him, and all it took was thirty seconds of her time at the information plaque.

She's enjoying herself immensely.

Another withering look is cast over her, and she presses her lips into a thin line. She won't irritate him further by being smug about her little treasure trove of shark facts. That wouldn't be very fair.

"But they've got such dead eyes," he argues, grasping at straws now. "I bet they don't feel anything at all."

Molly rolls her eyes, and he catches sight of it in the reflection of the glass, his eyebrows drawing together to form a scowl.

"Why did you bring me here tonight?" She's changing the subject, but as much fun as teasing him is, she still wants to know why he decided to wake her up in the middle of the night.

He can't have been that desperate for shark facts.

"Evidently to destroy all of my analogies," he replies tartly.

She smiles, watching the progress of a turtle as it skims along the bottom of the tank, its flippers leaving thin trails in the sand.

"But really?"

He pauses before answering, and Molly looks up towards him. The damp ends of his hair are clinging to his temples, his scarf still sodden.

"You've looked a bit bored lately," he says. The rounded shape of the tunnel give his words just a hint of reverb, making his voice sound impossibly deeper.

His words take her by surprise. She'd hardly noticed it herself, had been filling the time with autopsies and paperwork and trips to the pub and nights in with Tom. But she's been trudging along, she knows that now. She's been trudging, and Sherlock's noticed.

"So...you thought we'd break in to the London Aquarium together?" She lets out a breath of laughter, her front teeth scraping against her lower lip. He's a funny old thing. She wouldn't swap him though.

"Well you've had fun, haven't you?"

She nods, edging a little bit closer to him, but she knows that time is running out.

"Won't the guard be back soon?"

Sherlock shakes his head, dislodging a few droplets of rain from his hair. "We've still got a few minutes."

She doesn't want to know how he knows that - the answer is likely to be thoroughly dull, but she trusts his judgement.

"Give me some more shark trivia."

Molly obeys, casting her mind back to the words on the plaque.

"Blacktip Reef Sharks are viviparous," she says, and she can see his lips curve in his reflection. "And Nurse Sharks can pump water through their gills when they're staying still, unlike most sharks."

He nods approvingly, and Molly clasps her hands together in front of her. Her engagement ring digs into the flesh of her palm, but she ignores it, for now. She refocuses her mind on the present and forces her guilt down, out of her head, past her stomach, to somewhere around her feet.

She'll deal with it sooner or later.

"They can get through thirty thousand teeth in a lifetime," she tells him, forcing her mind onto silly nuggets of trivia.

"Without even batting an eyelid, I'll bet," he quips.

She gives him a stern look, but it doesn't last; his sly grin is too infectious.

"Come on," he says, taking her by the wrist and leading her to the exit of the tunnel. "Better keep moving."

The End