Sherlock Holmes knows he's a marvel. He's a bloody marvel and he's aware of that.
He knows that his brain is a wonder, and why should he be modest about that?
No one is going to give him a prize for that in any case (no, he's only given gallows and crowns of tin and laughing faces, green with envy and red with anger), and he's not going to hide himself.
Because if the world is made of plastic replicas that point at him their index fingers and peer at him with judging eyes, then he's going to show them that he's made of ivory and genius and that there's a whole world inside of his skull and an abyss into his chest—but he can live with it, without falling into it. He only has to be a bit careful when he walks on the edge (because he does, because he's curious and that dark hole looks so empty and so unfamiliar to him), and he has a strong sense of equilibrium. He knows that he will fall someday, but there are going to be a lot of dawns and sunsets before that day, and maybe—maybe—he will be prepared when that happens.

He knows that his brain is a super-complicated machine whose gears cannot just stop taking the world and analyzing it—chewing it, dismembering it—until it's right in front of his pupils, all broken and simple and stupid (and he pities it and envies it at the same time).
The world is shattered and it's crying, crying tears of shame and clinging onto his blue dressing gown, scratching his face with its sharp nails, trying to go back to how it was before he was born, before he picked up the chisel of science and the scalpel of logic, inscrutable and perfect and out of reach. But the world—this pathetic image of the world Sherlock has to see, this silly little girl in a white dress and with eyes that are red (no, scarlet) from crying—cannot hurt him, cannot really touch him, because if his heart is made of stone and his mind of diamond, his face is made of marble and it's not going to move (showing emotions is for the weak).
It reflects everything that is inside of his skull, behind his azure eyeballs: the gears. Oh, the gears.
They're cruel gears made of iron and steel and numbers and coldness and of a spasmodic desire to know and take and own and make things his possessions, all aligned like petri dishes on his desk, ready to go under the microscope's lens, ready to be observed, touched and catalogued.
They run and run and run and move and change, and eat everything that Sherlock sees, from the weapon that killed the victim to the love that brought an army doctor to his side. But they're not only a way to discern the world, no, they're a way to destroy it, and everything he loves and cherishes and cares about ends up being shattered into tiny fragments, as well as everything he hates and loathes and ignores, and he can do nothing to fix it (because, in the end, he's human).
The gears treat things and people like specimens and they feed themselves on specimens.

He knows that people would sell their souls in order to merely grasp the basilar concepts of that machine only to create copies and copies of it and sell them in shops and use them to solve their little, meaningless, idiotic problems, trying to improve their ridiculously common lives. They only even care about rubbish, and they would turn those perfect machines into rubbish, too.
They could be like him, if they wanted to. But their eyes are covered in lead and their eyelids sewn in red wire, their mouths speak the language of the fools and their hands clap the applause of the imbecile (and they make so much unwanted noise, he wishes they would stop).
When the people are not busy ridiculing themselves and looking at him as he was some animal in a zoo, they scream like devils on fire, filled with jealousy and envy and hate (the noise, the noise!).
They could be like him, if they wanted to. But their brains are not marvels and are not machines, no, they're made of mud, filled with stupid things, so barely used, so dead, so dead.
Sometimes Sherlock wishes he could enter those brains and sculpt them, carve into their synapsis the sparkle of genius and engrave in their neurons the fire of doubt. He wishes he could mold those masses of meat like an artist molds their first matter, but he cannot. And it destroys him.

Everything is dull and boring to Sherlock's brain: he can see the projects behind the things, the skeletons behind the ideas, the instincts behind the beasts and the sentiments behind the people. He can vivisect the world, but the world cannot see it because it's too busy thinking that he's a marvel, and too jealous to see that he's a broken madman, completely and utterly crazy, a statue made of ice with a burning heart and an aching mind, a walking wreck in a prison.
But sometimes the world doesn't think he's a marvel: it thinks he's a monster, a freak, an aberration, but he only lusts for knowledge and he will do anything to obtain it, from enduring the insults to piercing his wrists, because if there's a greater good, a good that he can die for, then that good is knowledge, knowledge that can feed his gears and make him live. He can't possibly allow the gears to eat themselves—and he knows that will happen if he stops working, if he stops thinking.
He can cut the world into pieces with his piercing eyes and his long fingers and line them up in tidy rows to his pleasure only for the sake of it, just to prove that he's capable of that, just to make the Earth less chaotic and untidy and asymmetrical and wrong. But he doesn't do that for that reason, no, he does that because he can't think of any other way to live, to act, to think, because he's afraid of his brain eating itself, of its mind engulfing its genius and of the blank that would come after that.
He can almost see that blank. Almost. Because he has a canvas into his mind, a blank canvas.

All is connected by thick and thin lines, everything is a dot in a blank canvas and he can write on it, add as many dots and lines as he wants, and it would still make sense because his brain is a machine and a marvel and something he can control. The canvas is never empty, and how could it be? Can Sherlock imagine emptiness? Can Sherlock really imagine it? Yes, he says, and it comes in a terrified whisper. He's shaking and he's frightened and he keeps writing desperately on the canvas, adding data and drawing thoughts, using chalk and tears and blood and paint and everything he can use, because everything—everything—is better than the void.
He has experienced the void before, but he was only on the edge of it (even if it felt like he was in its middle), and he became addicted to the danger, to the adrenaline. But quite a lot of syringes later he had understood that there was something wrong about it, because feeling normal—brain resting, mind keeping silence, eyes shut and heart pulsing—wasn't normal to him. He had to work with what he had, and what he had was a mad brain and voracious gears. So he stopped.
The small red dots on his forearms were forming a beautiful pattern and he wanted to see more of it, but he stopped, and it felt like vomiting and crying and agonizing.
But he endured it for the sake of knowledge. He still does.

Yes, he can control his mind (until a certain point). But he cannot control the world and this drives him insane. He cannot stop the world from being wrong and nonsense. Even if he can see beyond everything, even if he can make the world cry, even if he can skin it and collect it, this doesn't mean it makes sense. It doesn't. It simply doesn't and sometimes Sherlock finds it hard to breathe, and he chokes and gasps on the air that is made of molecules that are untidy and chaotic and just plainly wrong. He can't block the visions out of his mind, he can't help but deduce and find all the dots and all the lines and join them—and he wishes they would stop, just stop and be still and be quiet, and then he thinks of heroin and small red punctures and wants to see them again so desperately, but he can't, he can't. He cannot be normal because it would be weird.
The world explodes behind his eyelids and language stops making sense because it will never be able to express what he's feeling, the language dies and resurrects in only a few seconds, he sees the atoms and the galaxies and he can almost see the blank, the void and the gears; he looks badly for data, for something he doesn't know, and then everything can be controlled again (for a while).
He might be a marvel, but he's just a man and he's just a monster, and how can a man made of clay and a creature made of sickness fight against so many dots and so many lines? They keep rising and growing and they're not in even numbers, how can he bear it? He shakes and trembles under his burden, but he doesn't want the gears to squeak, so he goes on, like a beast, like a slave.

The world thinks he's a marvel, and the world is right.
The world thinks he's a monster, and the world is right.

Sherlock's eyelids are heavy and he feels sick and has the right to feel sick, but then a voice calls him back (calling his name, making him remember who he is) and he does come back.
He opens his eyes and he's sitting on his armchair and John is looking at him. John.
In less than one second his mind is hungry and it's working again—John is wearing a jumper he doesn't particularly like because Harriet bought it for him to feel less guilty about her drinking habits, and John is so full of sentiment and that's why he's wearing it, really, he's formidable, how can he even do that, having nerves of steel and a tender heart, maybe it's because he has no gears, Sherlock doesn't know but he will figure it out eventually because he cannot allow himself not to, John had a terrible day at work and he can see it in the curve of his lips and the expression of his eyes, how can people not notice this, it's elementary stuff, and yet they don't, how, how, and John doesn't either but John tries to, at least he tries, because if Sherlock has a mind of iron and a heart of marble, then John has a heart of steel and a mind of paper, because he wants to learn and he wants it so badly, and it's all moved by love, and how can he not fall into the abyss, maybe there's not an abyss in the first place, I should carve his chest to make sure, and now he looks worried and annoyed at the same time—, and Sherlock is so grateful to John for that he could die right now.
John's eyes are inquisitive but he says nothing, because he knows that Sherlock's mind races sometimes and he know precisely and exactly when it needs to be stopped before Sherlock does something incredibly stupid just for the sake of it, for the sake of using his brain.
John knows how to stop the void.

Sherlock Holmes knows John is a marvel. He's a bloody marvel and he's aware of that.
John Watson is a marvel in a complete different way, though. His mind is not made of gears and it's not a machine, but still—they kind of belong to each other and it's wonderful, it's wonderful that Sherlock is owning him because he's a possession he's quite proud of.
And if John's his possession, then Sherlock wants to study him like he has never studied anything before. But he knows that what he wants is wrong and he knows that it would ruin John.
He wants to peel the skin off John's skull and place it on a canvas and admire it, he wants to saw John's skull and place the fragments in a bowl and play with them sometimes, he wants to take John's brain and cut it into pieces just to see why John can't see what he sees, he wants to take John's heart and watch it while it pulses, he wants to fill bottles with John's blood and assimilate it just because it's his, he wants to cut away his limbs, he wants to do so many things and none of them is even remotely right or legal. He wants to give John an autopsy while he's still alive, and he wants John to do the same thing to him. It would be marvelous, wouldn't it?

He wants to disassemble John and then fix him.
He wants John to disassemble him and then fix him.

He wonders what John wants to do. He's pretty sure John doesn't want all those things because John is normal and that is both a curse and a blessing; Sherlock needs John to be normal because he needs John to stop the void and he needs John to make him know what is wrong and what is right, because he knows everything but nothing makes sense. John can't understand him but that doesn't mean he cannot complete him (they fit so well, don't they).
Sherlock cannot love him in any other way. Because he does; he likes walking on the edge of the abyss too much not to know that. It's not romantic, it's not sexual, but it's love. Not the right kind of love, not the normal kind of love, but there are so many types of love and so many types of everything that it doesn't matter, it just doesn't. How could it possibly be important?
It's two soul mates saving each other. It's two lives tangled up and mixed, it's two marvels killing and resurrecting each other over and over. It's something unique and terrible and wonderful at the same time, and Sherlock loves it and he knows that John loves it too, because he knows everything without understanding it and he needs John to translate everything for him.
Sherlock cannot love him in any other way and John cannot either.

They can try to be happy while hurting each other—John being a compass and giving the world sense and being a heart, and Sherlock giving him crime scenes and battlefields and being a mind—, they can try and fail and try again because they're bound to linger on and bleed.
And, oh, they love it more than the air that they breathe, more than everything else in the world, because they are one and they're made for each other, and that's an abused idiom but Sherlock (Sherlock that hates language because it can't express anything, Sherlock that cannot speak of the dots and the lines) can't think of anything else. And John cannot, either.

Sherlock notices John is still looking at him with the same expression. He knows.
They both smirk at their soul mates, soul mates that are hurting and healing each other.

Sherlock Holmes and John Watson are two marvels, and they know it.
Sherlock Holmes and John Watson are two monsters, and they know it.
What the world thinks doesn't really matter.

Sherlock picks up his violin and starts playing. John closes his eyes, and listens.