It's only a few hours after dark when Sherlock finds his way to the shipping yard that Jim has chosen. That has left more than enough time to finish everything they wanted, leave loose ends neatly connected so that no part of Jim's plan can come undone, ambient isotopy of the way he thinks, letting what he plans deform into what becomes reality.

When Sebastian returns John to him, he's still moving, pain overcoming his desire to slip into unconsciousness, and Jim watches him writhe, thinking that John, too, makes a fascinating pattern, simple Reidemeister move to turn him from pawn to player, because there are hidden depths there and Jim wants to plumb them all.

But later. He can take his time. There will be years, if he wants there to be years.

For now, he lazily checks Sebastian's handiwork – looks just like all the other marks and he decides he isn't worried; there's no reason they'd pick up on this one before any other, and Jim can, after all, fix it so that no one else will call attention to it either.

Sebastian has been exceeding expectations ever since he brought John home with him. He's been rewarded, yes, but this is very, very good, and perhaps he deserves more than just the leavings of the game. This is delicious – Jim runs his fingers over and over the mark, safe in the knowledge that there is no way John is lucid enough to recall his attentions – oh, yes, this is why he hired Moran, not for assassination and not for the subtle cleanup afterward, though he is gifted at both, but just this sheer talent for the manipulation of skin and sinew into bright, new, fascinating patterns.

Watching him work is a joy; seeing the results is insight.

John has to be carried into the shipping yard; that, of course, was to be expected when Sebastian began. Leaving people intact is not something with which he concerns himself – functional is a stretch sometimes, even when Jim forbids him to kill them – and although the point was never to remove John from the equation, there's nothing that says he has to be returned pristine.

Jim sends a knowing look in Sebastian's direction. 'Pristine' is hardly the word for the state of John Watson now. At least his face has been wiped clean of blood. Sherlock is interesting and John has become so, too, and Jim wants to play more – so John has to look presentable when he's returned. (The façade will only last until he's given back to Sherlock, but the detective is blind when it comes to John, and stupid, so the lie will be enough to distract him.)

Sherlock will take him to Bart's when they are finished here, Jim decides. With the swooping signatures of Moran's craftsmanship across his skin and deeper, brutal intrusions onto the manifold of John, there is no way he will not go for medical attention (though what good it will do is still debatable; Sebastian's scalpel is more subtle than any of theirs), and Bart's is where the fewest questions will be asked.

This works out well for Jim, who has already identified a weakness. He sends a runner with a message to the hospital, to a specific doctor who has too many secrets – a death knell under Moriarty's practised eye. Although the message is designed to both threaten and bribe, he knows that only one of those two will be necessary; the doctor he has in mind is neither brave nor intelligent (not John, his mind whispers, no, not like John), and the threat alone will shatter him like glass.

How ordinary; how distasteful.

Sebastian is the first to spot Sherlock, running up an aisle formed by the rows of shipping crates. He fires a warning shot – nowhere near the detective, but a pockmark appears in the concrete at his feet, and Sherlock stops running.

"John's not with me, Sherlock," Jim calls out, sounding far less interested than he truly feels.

"Where is he? Why have you brought me here?"

"Don't worry," and even Jim can't make that sound sincere. "I'll let you find him soon."

Really, Jim has no reason not to give John back now. He's served his purpose, and the new game that will start when he goes home is so much better than anything they've done so far that Jim can hardly wait to see them making their first move.

But no. Sherlock has to believe that this is for the sake of something else – a game in its own right, rather than simply an opening gambit. Jim can't make this too easy for him now.

"Do you know how much blood is in the human body?" he asks.

Sherlock's voice is cold. "About five litres."

"Mmm, about that, yes." Jim has derived an equation for his next question, but Sherlock, he knows, won't be nearly as accurate. "How much do you think John has left?"

It isn't an entirely idle threat. Sebastian may have limited himself to superficial damage – mostly – but he knows where to find delicate vessels, leave them ragged bundles, epimorphisms of their former selves (for every gentle stroke of knife, an equivalent bloom of slow, deep red; four-colour theorem of John: pale skin, blond hair, beige jumper, and the blood). If John does die, it won't be quick (but Sherlock doesn't know that), and it certainly will not be anything remotely resembling painless, but Jim is counting on Sherlock to have the motivation not to let that happen.

After all, it would be such a waste.

"If I were you," he says, drawing out the words so that he can watch Sherlock twist under the painful slowness of it, "I would be looking for him. They take so long to train, you know, I'd hate to have to find another one."

Sherlock stares at him for a moment, then spins on his axis and lunges away. He's stopped, again, this time by Jim's soft voice.

"Running won't be enough."

The shipping yard is massive, thousands of containers stacked two and three deep. Sherlock could run all night and not find John, and if that's what he does, then the new game is over before it's even begun.

"He's traceable," Jim says, "connected." The entire shipyard, laid out in a powerful digraph. Jim saw it instantly, his mind solving degrees and dominations almost before he realized how beautiful he could make this if only – and he had to have some of the containers moved, some vertices adjusted to yield directed arcs, but now it's kernel perfect and there is just one source vertex, just one root.

He holds a piece of paper up between his fingers. On it is a category theoretic definition; it yields the binary function that models on the graph. Just this one simple solution and Sherlock can have John back. Just this one small, elegant piece of mathematics. He lets it flutter down; Sherlock snatches it before it reaches the ground.

Jim doesn't know why the universe is so overtly fond of him – but here he is, he's wrung from John both agony and mathematics, and now Sherlock is standing in front of him and he has to solve a personalized challenge with the lemma Jim has given him. There couldn't be a more perfect ending to the game than this.

Sherlock drops to one knee on the asphalt, clutching his mobile desperately as he taps on the keyboard, searching for the knowledge that will let him understand the scribbled symbols.

Jim walks away, his own phone in his hands. He's activating the new feed, data streaming in; it falls into delicious fractals and he drinks it in, this pure, exquisite theory of John. Self-similar, his heartbeat pulses through the numbers. Jim can see everything, all of him at once, hear every action of his body, every breath and beat and tiny movement. Unconscious, John is fascinating. Conscious, he will be more beautiful than any problem Jim has ever solved.

The iterations change, become complex. Sherlock has found the right container.

Jim watches the chaos game play out on the tiny screen. John won't wake up – no, not in the condition Sebastian left him – and, Jim thinks with pleasure, he's probably much better off if he doesn't, at least not without the influence of heavy drugs. He knows Sherlock will take him to the hospital, where Jim's hand-picked physician will examine and scan and treat and never once mention the tiny shards of metal, silicon, the wires deep under John's skin. It's lucky, John's old war injury; Jim couldn't have designed it better if he'd tried, because there is no way that John can feel what Sebastian has left behind, and so he'll never know.

Jim has never understood Sherlock's love of experimentation. He's never quite grasped why Sherlock is so easily placated by the limitations of applied science, orthogonal to the abject freedoms of Jim's theorems, pure abstractions that allow him not just to navigate the universe, but to outwit it. This, though, this tiny device reading every subtle signal of John's body and gathering the data into ever-changing patterns, functor from the concrete to the ideal, gives him an understanding of what Sherlock sees in it. Information is knowledge, knowledge is power, and when Sherlock cannot rouse John, Jim knows immediately. When the detective picks up the other man and carries him, desperate to get him somewhere where he can be helped, Jim knows immediately. He reads the beat of Sherlock's heart against John's shoulder in the added frequencies of the recursions, in the changing shapes of the constructs. He sees the hitch of Sherlock's breath in the irregularities that shift the fractals, ever-adjusting continuity of statistical proofs.

This is so much better than a face on a CCTV camera; it's so much more alive than his snipers' reports every half hour. This is so much more than just an experiment – Jim is not testing John, he is owning him, every single nerve and fibre, every cell of his body singing to Jim through the numbers.

Sebastian has given him control as well. He's left everything energized inside, so that if Jim really wants, he can make John wake up in the dark, electric nightmares flickering in his mind, the result of tearing pains in his left shoulder. Remnants of the war, he'll think, and never guess, and Jim will smile and watch the numbers jump as John bites his lip to keep from crying out, and he will go on torturing John in the night, because he can, because if he can't have this new toy to himself, he may as well continue destroying him for Sherlock.

That's all there, and it's thrilling, and Jim knows he won't be able to resist. But that's for later. For now, he is content to watch them both dissected into numbers, reading every tiny tell-tale signal of their bodies, everything they don't want him to know. He is already seeing weakness, and in so much more rich detail than he ever has before. The devices are simple, certainly; designed for nothing more than light reconnaissance and torture. He's used them before, to keep his… assistants subdued. But doing this to John, secretly violating him and Sherlock, too, this is a new and fascinating use for them.

It's the sort of thing Moran's twisted mind understands all too well.

Jim hands him the mobile phone, and Sebastian looks questioningly at him. One nod – permission – one button is pressed, and Jim can see the spikes of feedback skitter all over the screen, his mind calculating the functions behind the new peaks even before he catches up consciously and realizes – this is what John's pain looks like, and the thought jolts him to the point where, recklessly, he brings his finger down onto the screen.

John's unconscious body jerks so hard the readings pick up Sherlock's pulse and breathing rate; he's terrified, and this is glorious – John's agony and Sherlock's anguish, all reduced to systems of polynomials, proofs that Jim can write, topologies that he can map. This is a whole new field of mathematics, one in which there are no publications and his discoveries will be written only for himself.

That's enough for now. He pockets the mobile; he's satisfied, he's pleased, and it's a rare enough occurrence that he'll savour it slowly. He does have restraint, when he wants to have it, and the possibilities in this are something Jim knows will keep him from being bored for a long time.

He lets Sebastian take him possessively by the hand and lead him from the shipping yard back to the waiting car. His right-hand man's actions have merited reward, and Jim is more inclined than he has ever been to give it; after all, they have the time. They have all the time they want. Jim's thirst has been slaked.

He can solve Sherlock and torture John and none of that is dull, and really, that's what all of this has been about.

The mobile phone is heavy in his pocket as he runs one finger delicately over it, a smooth gesture equal parts promise and threat.

Oh, yes, this game will be good.