How frail the human heart must be...
an instrument of glass
Sylvia Plath

Once, you had an exact definition of what a heart was. You know what it is, have poured over the printed diagrams in the pages of medical books – red for arteries, blue for veins – in your desire to learn, and of course, being a consulting detective – the world's only as a matter of fact – you've seen them in the flesh. Human hearts, displayed in a Y-shape frame on a steel table, mounds of muscle that all look the same once the owner is dead. You take it for granted, don't you, that it'll keep going. The core processor that you consider secondary to the hard drive of your genius, that survives the nicotine and the sleepless nights and the lack of food, the cigarettes you once chain-smoked for a case that lasted three weeks, and after that only habitually, and every bullet that has been a near-miss.

That hollow organ responsible for pumping oxygenated blood around the body, situated left of the breastbone, that's right isn't it? If someone asked you to define a heart, you know what you would say. You could mention the four chambers; left and right atrium, right and left ventricle, and then – before, before your change in priorities, when you thought you knew what the world might throw at you – you would have focused on the minutiae of the topic; pericardium, tricuspid, mitral, pulmonary, aortic, contract and relax, contract and relax, seventy two beats a minute on average. Put a cold stethoscope to the skin, listen to the sound that restless muscle makes – boomboom, boomboom - the opening and closing of valves, the vibration caused by the movement of blood. You understand these concepts. Scientific, precise. An amalgamation of numbers and data, centimetres, volume, density, and it is nigh on impossible to misinterpret.

But then it's not as simple as that is it? Nobody sees things quite like you, your comprehensions bounding ahead while others stumble, breathless, a mile behind, but oddly, their funny little brains understand things in their funny little sociolects and quirks that you don't. But that's ok, you can deal with the other meanings of the word. They are abstract concepts, most of them, insensible idioms used by the masses, but you can work these out. It can't be too hard can it, your marvellous brain of fluttering pulsing synapses can perceive these.

You understand that it is one of the suits in a card game, that you can know something off by heart, can have a heart, can have your heart in the right place, or even, strangely, can have your heart in your mouth. You can be heartbroken, heartless, heart-sick, light hearted, you can lose it, or set it on something, you can take heart, or wear it on your sleeve. Which, as an idea, you feel is quite idiotic. It could get dirty, become lost, and that's not mentioning the fact that wearing a human organ about the size of a fist as some sort of cuff-link would be monstrously unappealing.

Oh, but you didn't count on the rest of it. The puzzling difficult humanity of the concept, based not on comforting rational, but on emotion. Feeling. It is all well and good to categorise these things into anatomy and lexis, but in terms of intuitive feeling, of sensation, you are out of your depth. You've never had someone's heart before, wouldn't recognise one for what it entails, means, promises, and you've certainly never given it to anyone. You wouldn't know how. It sounds macabre, unnecessarily dramatic. Reaching into your thorax, pushing past sinewy overlapping muscle strands and cracking through arching bone-white ribs to pull from there your still beating heart to pass over to some worthy person, that would be detrimental to what you were overall trying to achieve. Even as a metaphor, it falls short.

And anyway, the whole concept it is tied into – that of love; that motive for murder, stronger than blackmail, vitriolic reasoning that inspires people to kill – is relative. How do you know that you have given someone your heart anyway? And if there is a gap, a fatal niche in your chest where the organ has been taken, how would you recognise if the object of your affections wants the proffered item, or if they'll just take it and disregard it moments later, allow it to gather dust?

What you first find out about love, you do so in a landscape of rubble and water. That heart of yours still beating; thrumming with adrenaline, not the chemical of the game, the glorious game, but of panic, the twisting in your chest you can't identify. That heart of his not doing the same; floundering, shuttering, a once proud thing reduced to stubborn inactivity, beneath hands that are yours but are covered in crimson, hands that do not shake but should, somehow that would seem fitting, hands that are trying to pound a pulse back into him.

He is still, clothes all over his body sodden, and he's not supposed to be so quiet.

Wake up. You always want something from him, are rarely grateful, but if he could give you this, and he sat up now, spluttering chlorinated water and blinking rapidly like he's just been born again – well, then you'd be appreciative. Thank you, because now I can breathe again.

Steam rises from the liquid splashed onto charred cracked tiles, back lighting your scene, water evaporating, hissing, and bricks and part of the structural layout of the building collapse into what little liquid remains. Or else the splintered strips of changing room walls, plasterboard and paint, tumble from their mooring, force dust and ash airborne to swirl and cling to your sodden coat. Everything about you is dirty. Your ruined clothes, jacket lost to the water, white shirt sticking, drying against skin, you've lost a shoe somewhere along the line; your hands, smearing a trail of dirt, useless, useless things that move too slowly, you don't quite know what to do with them; your heart, boomboom in your chest, traitorous.

That is not your problem now. This is. This stupid man here under your hands, this brave, stupid man, who is making you frightened, making you lose control, is making you feel things you didn't think you were in touch with any more.

You are burning. In your chest, something is still on fire.

You repeat his name. Transposing it on the silence. John. John. John. Like a mantra, like you've memorized it on a scrap of paper, a well-thumbed script and tonight was the big opening night and you've blown it; it's like a controlled experiment you messed up because you were too eager, too liberal with components and chemicals. You want to go home, home that's only home when he's in it. You don't want this place to be a memorial ground. On this ground, Sherlock Holmes lost his heart, and John Watson lost his life.

John. John. His name cuts through every plan, every equation, formulae dashed and unnoticed, the numbers wrong, they don't add up – scratch them out then, let this make sense in terms of things you understand – compute the right data. John. His name the way you say it is a heartbeat all of its very own.

This part of the tale is not glamorous, and although you worked it out, you didn't win. What were you playing for anyway? This part of the story has you, half destroyed, slender limbs folded into something that is asking for forgiveness, awkward and unfitting, asking for something you've never wanted, all the human affection that people expect you to expend on their behalf narrowed down in its focus to one man lying on his back and not listening to you, driving your hands against his chest like you are punching him, wanting to leave a bruise, a mark where blood vessels have burst – look what you did to me, open your eyes so I can scream at you.

When he finally does, there is a sheen of a smile on his face that placates the panic on yours, and you forget to be mad at him.

Then, later on, fast forward the boring bits, orange shock blankets and hospital, Scotland Yard, questioning and statement taking, you are both back at Baker Street. You return to what it was like before, locking out the amateur things you still don't understand; you bounding, computing, busy being brilliant and forgetting to eat, to sleep, while John – limping for the first couple of weeks after hospital discharge, using his cane for a real injury, but you wait for him to catch up even if you do fidget and wish he'd hurry up and heal, so he can explain to you the answers to your questions – follows on behind, your ghost, a fleshy shadow that shouts at you when you take risks and feeds you and orders you to sleep, someone to care about your well-being when you forget.

Perhaps you managed to convince yourself nothing was different, maybe knew what it was that had changed, but also convened a meeting where you decided that there was parts of you that weren't ready for what was new, the unknown. But you find yourself looking at the doctor these days like maybe you wish he'd been frightened away by it all, that maybe you wanted him to blame you and never forgive you, but at least he'd be away, he'd leave you alone, he'd be safe.

You talk, but not about the things that matter, not about the things you want to, and every day you wake up, and wake up, and wake up, and every night watch him go to bed and still say nothing. You don't know how to deal with this, but this is the brink of something, and you are teetering on the edge while someone sniggers I told you so.

You don't recognise you gave him your heart until it was irreversible. A convergence of moments where you cannot go back, a ratio that was never weighted in your favour, something astronomical and beyond you, better than you, bigger than you, like stars, and death and the glassy skin of a swimming pool.

You simply handed it over, a withered misused thing, didn't say anything because you didn't have the words you needed for this enterprise just yet, entrusted it into his care with not even a thought. You didn't think you could be so careless as to lose it to someone; losing implies lack of control, and that's not you, not you at all, but then again did you ever really know yourself and anyway, he is changing a lot of things about you without meaning to. Smoothing the jagged parts of you, and when you spring around the latest crime scene, reeling off your deductions because really, it's so obvious, gesticulating with your hands like you are forming the flight patterns of birds in the air, his

smile makes you want to be the man he thinks you are already.

The heart you pass over to his care is not even worth having, yet instead of it being a burdensome organ formed of chambers and muscle passed over like this could mean anything other than what you don't want it to, it is more subtle than that. No one defined this for you, you're allowed to get this wrong. Heart's, you find out, take obscure shapes, can be tangible or immaterial, ephemeral, but always with a lasting intent. They always mean something, a dizzying gravity of importance, and that's what you were afraid of.

The heart you give him is the credit card you rarely use, when he's too proud to ask and too embarrassed to mention it. You give him your heart by showcasing for him the city you love so much that you want to share it, its warrens, its hidden things and hidden people. You point out the stars to give him that memory to smile over. Your heart is in that scarf of yours you lend him when the streets are cold and wintry and you dragged him out in that flimsy jacket of his. It's the things you let him see, it's the chase you let him feel, light-headed as you run, light-hearted even, it's the first violin piece you play solely for his benefit.

And the things you give him, like individual letters that spell out a universal truth, an impatient frightened question, he accepts, and you are worried he doesn't know what this means. What he's letting himself in for. Because it will happen, maybe not today, maybe not even tomorrow, but what you want, you inevitable get, and that ideal takes root somewhere in your chest, is one of those rare hopes that can be brilliant and terrible at the same time. The things you care for, you corrupt them despite your best intentions, taste their potential then find that place in them where you can slip through the skin and destroy them from the inside, you ruin them so they hate you, and it's only a matter of time before the same happens again.

But it doesn't. Instead, John Watson takes your heart in tender hands, sees the evidence of your affection and does not flinch even though he can see how hungry, how desperate and immature and cracked it is. And you notice then that he's given his to you already. They were the things you never deleted. His heart was in cups of tea and irate-but-not-really texts, in the insistence that you sleep, or the meals he took you out for in the hope you'd have something to eat.

His heart took on the form of the scarf you forgot in your eagerness which he remembered and gave back. It was in the words he said to you, making conversation, and the things he never voiced aloud but you understood, conversing in nods and implicit trust, it's that time someone punched you and he swept in with tight eyes and a grim roiling fury, and punched them back, it's in everything he's said in your defence and every unspoken show of solidarity. His heart is a dented thing like yours, damaged from war and lack of care – no, they are not dents, they are slots where the two of you click together, and now he's given it, he can't take it back, but it's clear he wouldn't want to.

You want to say Stop, don't bother, really, I don't know what to do with this, I might damage it and then what happens, I don't deserve it, I'll break it and then you'll end up breaking mine, but the moment is never right and the words sound wrong. So, you take his heart and try and care for it as best you can. It's not a question of owing him something, there are no debts between you, it's more like declaring something you both know, like the words to the songs he sings in the shower even though you tell him he's tone deaf and bang on the walls, like those smiles, flighty quick things to let him know without a doubt that he has something of yours and he can keep it. It belongs to him now, and anyway, you've got his to keep you breathing, another muscle to pump blood, another set of valves, pulmonary, aortic, and they seem stronger than your own ever were.

The first kiss you take from him you steal like a thief, like taking something precious before withdrawing again, eyes darting, guilty, maybe I did it wrong. This is your big scene, only you've forgotten the lines, but the camera is still rolling, whirring, and if he laughs at you, you wont be able to handle it. He does smile, but it is an invitation to repeat your crime, leaving the door wide open to let you back in, so it's not burglary anymore, it's the best sin you've ever committed.

You want something to call your own, something to keep, to hold, to love, and most of all want him, and so you take his heart that he offers and kiss him again, notice at the same time that he's taken yours completely from you as payment.

You don't mind that much. You saved it for him anyway.