I neither own nor profit from any of these characters; they are the property of Sir Arthur Conan Doyle, Steven Moffat, Mark Gatiss and the BBC.

If you see something that you think ought to be changed or improved, please feel free to let me know, if you'd like. Constructive criticism is always welcome.

De-anon from kinkmeme prompt: "True to the canon, I want Jim to be this brilliant scholar who writes papers and does absurd math problems and shit when he's not blowing things up and/or flirting with Sherlock." This is... not exactly that, but sort of.

A/N: Because I am a massive nerd, all of the mathematics presented here is real and correct in context. If you find an error, please let me know!

folha5eca has created a beautiful cover for this story here (is . gd / zsgch9). Please go and take a look - it's stunning!

James Moriarty cares about three things: mathematics, the game, and understanding what makes Sherlock Holmes tick.

When he can combine two of those things – glorious. When he can combine all three…

He thinks of that sometimes, while Sebastian is doing unspeakable things to him, and Sebastian can always tell, changing his rhythms, pulling him back jealously until Moriarty winds his fingers through his hair and tugs, and it's enough to distract Sebastian for a moment.

Sebastian should know by now, he thinks. Of course no one could occupy him the way his favourite problems do – at least, no one whose brain he can deconstruct and lay open, reading the neural pathways like so many fractal patterns in his mind. And that doesn't leave many options – just one, just Sherlock Holmes. Their sets are isomorphic, his and Jim's; one to one. And so Jim wonders.

Sometimes it seems to him that they are the identity functions of one another, their brilliant brains mapping onto each other's images like two objects in a psychopathic groupoid.

Other times, it seems almost as if Sherlock is the right brain to Jim's left, which would seem absurd to anyone who knows Sherlock. But it's true – whenever Sherlock does his 'science of deduction,' he relies on the connections his mind makes across the entirety of the crime scene and his vast storehouse of knowledge. He knows what people feel and how they react and why they do it, even if he himself does not subscribe. Jim knows none of that, and doesn't care. Jim only makes things work.

Dear Jim, please can you fix it for me…


He and Sherlock have so much in common that they might almost be friends, if they had friends, and if they didn't hold one another in such contempt that they share everything from opposite sides, Sherlock over a body Jim has given him, a gift, and Jim over grainy surveillance tapes that Sherlock doesn't know exist.

Sometimes he thinks it would be wonderful if they could share this too, the madness and the mathematics that are constant in his mind. But there is one obstacle to reaching Sherlock's vast and complicated brain, one simple switch that must be catered to.

Sherlock will only care about things that are relevant.

So Jim will have to make this relevant, too.

"I need a body," he says to Sebastian, already sounding bored. He is bored – this is just the rigmarole, the opener to the dance. "And kill him quietly. I'll need to do it loudly later."

Sebastian nods, starts to slide a knife into the sheath hung at his belt, until Jim's hands stop him.

"No, no, no," he says. "I'll need him to bleed as well, when I'm ready for him. You can be a little cruder."

Sebastian finally leaves with a vial of abrin and a set of tools. He prefers to do his work by hand, but this time they need something else.

He does well. Jim is very pleased and lets his fingers trace a map of complicated functors on the smooth skin of his subordinate's bare stomach. Sebastian gasps.

Later, Jim plots out every point of blood around the body his right-hand man has prepared for him, smooth, continuous curve of evidence if only Sherlock sees it. Each drop precisely positioned, a pattern, an equation there to be interpreted, and maybe he is rather showing his hand a little, but he wants the message to be found.

And as he places every tiny silent witness to the crime, he smiles.

Some might see what he's doing and suggest that it is Jim who is the artist, Jim who is the right brain. Those people would not live to see the completion of Jim's work, because they are wrong, wrong in a way Jim cannot tolerate and never will. Jim is the science and the logic, and it's more than a life's worth to suggest more to it than that.

They insinuated to him once, when he was very young, that the duty of a professor was to teach. He was given a class, a horde of gaping simpletons in their first year at his small university, and he stood in front of them and surveyed them in silence.

Idiots, every one. He didn't even need to lecture to know that.

"Tell me," he said, "about the use of the conic section in determining the dynamics of the orbit of an asteroid."

They stared.

"Tell me," he said, making it easier, giving them questions he could answer in his childhood schoolroom, "about the generalization of the binomial theorem to powers of sums with n terms."

They stared.

He slammed his hand down on the lectern. "Tell me," he shouted, "why I should stand here and give you knowledge, just give it to you as if it were something you deserved, while every minute I spend in this room is one I don't spend doing something interesting!"

He didn't lecture again. It appeared for a brief while as though they might take away his appointment, but then he published the book.

The first paper had been impressive enough, the work of an undergraduate who should not have had the ability to consider the problem, much less solve it. On the power of that paper, he had been promoted through the ranks, through graduate school, to a professorship, to a comfortable lassitude where he could spend his days in thought and not worry about other people's messy, human needs. But the book, the book changed everything.

It was a complex work, so multifaceted that it had held even his attention for the span of time needed to write it. And when it was finished, it was perfect, an elegant theory born of an elegant mind. It was read and discussed by every mathematician who considered himself worth the title, but there was one thing it never was – understood. Reviews praised it blankly. Old boys of the mathematical colleges at Cambridge discoursed on it in lofty tones, until he, sitting unnoticed in the dark corners of lecture halls, smirked and asked them questions that left them without a response. The book was enough, even, to stave off the whispered conversations that had begun whenever he was near.

They never raised the subject of his lecturing again after the book was published, but by then he'd lost his interest in acadaemia – everyone was so boring. He quit of his own accord, and mathematics became part of the game, part of his toolkit.

Mathematics became the language he used to try to get inside the mind of Sherlock Holmes.

'Professor' Moriarty has always sounded ridiculous to him. A mark of respect, they told him when it was bestowed, but he doesn't need to hear the simpering tones of false deference in their words when they speak to him. No, he doesn't need that at all.

He likes a very different kind of respect, the kind that shows itself in the tremor of a voice, inching out the words it wasn't made to say. The kind that speaks to thick veins of adrenaline, running lightning-quick beneath the surface map of neurons. The kind that chokes and pleads and struggles, all those quintessentially human responses, all those things that are so messy and distasteful, and yet, at the same time, so delightful to control.

No, he knows what it is to be respected in the way he finds most thrilling. And so 'Professor' became Moriarty becomes Jim, and the more unpretentious his identity becomes, the wider his smile twists across his face when people make the wrong assumptions and, inevitably, pay the price.

Professor Moriarty publishes mathematical discourses, moving more and more these days into the realm of computational psychology as Jim tries to decipher Sherlock's brain.

Jim publishes his newest findings in the field of Sherlock, writing them across the skin and bones and blood of victim after victim, emblazoning them on the ravaged skyline when the emotions roiling in his head are too much for a murder, and a bomb and shock and flare of brutal orange fire are needed to scream his latest anger to the skies. On those days, Professor Moriarty never has a chance.

But even Jim will not forget his roots, and so the name of Moriarty has two meanings. One is the quiet mathematician who submits elegant proofs with strange, subtle, hinting titles and hidden twists of words, all there for Sherlock to find, if only he ever looks. And how delicious, thinks the other Moriarty, Jim, when Sherlock finally discovers all the deaths that could have been prevented with a brief glance at the newest articles in the Acta Numerica, the tiny flaws, the tiny clues… and best of all, right at the beginning of the trail, his name.

These clues were meant for you, Sherlock. You could have found me, could have stopped me, could have saved them. But mathematics? No, not really your area.

As is to be expected, every so often, Sebastian grows sullen and unwilling to distract him.

He does damage control and goes to his best employee, offering a measured touch that's never quite enough. Sebastian tells him, "I see through you. Go away. Go back to your sums, go back to Sherlock," and then Jim has to treat him roughly to win back his affection. Sebastian likes that; he always has. He used to like being ignored, too, but lately it seems Jim does that too well.

"I'm not like them," Sebastian says, waving his hand in dismissive gestures at the snipers Moriarty keeps on hand. "I know you better. Come away from all that, I have something for you."

What Sebastian has for him is predictable, follows the laws of idempotence. Sebastian is the closure operator to all of Jim's twisted fantasies, the Kleene star that puts an end to sick imaginings – the things he'd do to Sherlock, if, if – but it always ends in Sebastian, angry and demanding, taking everything Jim's willing to give (which isn't much) and leaving him frustrated and surrounded by the freshly-scattered papers of his latest theorems.

He crushes the crumpled lines of writing between his fingers, and on those nights, there are new bodies for his games.