The day passes in the agonising slowness of waiting. John spends some of it sleeping, trying to make up for the lost night, but Sherlock can't rest. He paces, between the window and the kitchen table, over and over and over again, counting his steps each time, then counting the number of trips, twisting his fingers into knots as he goes.
He's still at it when John wakes, and even John's hand on his arm is barely enough to slow him in his circuit. John lets him go, biting back his protests. Doubtless he understands this behaviour is a substitute for more destructive means of coping. At last, later in the evening than Sherlock would prefer, the phone rings and he is freed.
They rush to Bart's where a package and two soldiers are waiting for them. Two large soldiers; Sherlock can feel their hulking presences tower over even him before they speak.
"Yes, yes, Official Secrets," he snaps, scrawling a signature on the proffered clipboard without bothering to ascertain whether he is anywhere near the dotted line. "Now, run along back to daddy, we've got work to do."
It's very likely only the diplomatic intervention of John that prevents them from doing something nasty to him, but he hardly gives it a thought. That's what John's for, isn't it? Either way, they eventually piss off, with a stern parting warning that Sherlock barely notices.
This is the difficult part, he can hardly have anyone else involved in the analysis, but John's no chemist and Sherlock can't use the equipment, he'll have to direct John, thank God Molly's not here, she'd trip them up in her eagerness to be useful, best off just the two of them, really, even though it will be slow going…
"John," he says sharply, interrupting the doctor from whatever he's been babbling about – probably something on how he shouldn't make enemies in Special Forces. "Can you do as I say?"
"I think so," John agrees. "But really wouldn't it be better if we got someone in who—"
"No. Now, first I need you to read me the data sheet that came with the sample."
John does so, haltingly. Sherlock lets his mind go to the pristine laboratory he's created inside it for this purpose, building a model of the drug atom by atom and chain by chain, a super-scaled three dimensional molecule in his head.
It's clever, so clever, an organophosphate base with bromides linking rings he recognizes from virtually every common psychoactive drug known to man, LSD, THC, MDMA, he can see exactly how it would slot into the fear receptors, how it would trigger the adrenaline spike, work its way subtly into nearly every part of brain to produce complex and vivid hallucinations, paranoia, a complex molecule but so simple really and when delivered via aerosol nearly impossible to combat…
"Got it," he tells John abruptly. He can imagine the faintly puzzled look John must be giving him now, unaware of how clearly Sherlock can visualize the string of chemicals he's just read off.
"Great," John says slowly. "Problem, though. I might be wrong, but I've got your blood tests right here and there doesn't seem to be any sign of this is in your bloodstream. Maybe it's not the Hound drug after all."
Sherlock frowns. He'd hoped it would be that simple. Then again, if it had just been the drug in its raw form effecting him, the effects should have been diminishing over time, not like this strange, belated blindness.
"No, I know we're on the track, if only I could see, I could work it out, I know it!" Sherlock slams his hand down on the bench in frustration. "It must have to do with how I metabolised it."
He makes John take more blood, and gives him a list of all the possible metabolites he can think of to screen for. Then he has John run tests on the compound itself, solubility, toxicity, reactivity to other chemicals Sherlock might have been exposed to. It takes four time as long as it should, Sherlock using his mental lab to guide John in what to do and John, clumsily, obeying.
Nine hours into it, and they are no closer than when they've begun.
"That should have formed a precipitate," Sherlock continues relentlessly. "A white one. Did it?"
John sighs tiredly. "Yes, it did."
"Good! Now add ten millilitres of potassium chloride to the solution." Sherlock hears drops go into the beaker. "Well? It should be blue. Is it blue?"
"No, it just turned cloudy," John answers.
"Damn!" Sherlock snaps. "Are you sure you didn't use potassium bromide instead? Because that could—"
"Sherlock, I can read," John growls at him. "Look, I can't keep this pace up much longer, particularly since I don't understand what the hell it is I'm doing. Have you learned anything at all from all this?
He's learned that if it is the Hound drug in some transformed state that's cost him his sight, it's not going to be easily neutralized by any of the fifty simpler measures he can think of, and that it's not likely to run its course without intervention, whatever its done to him won't fade away, it's going to require some kind of active reversal, and it's not going to be easy…
"Some. Not enough." Sherlock admits.
"And you still feel like this has to be the cause?" John asks.
Sherlock nods. "It's the only scenario that fits all the data. Even if all the data doesn't quite fit it yet."
"Good enough for me." John comes over to him and slips an arm around his waist. No one's around and it's comforting to feel him physically again after hours of shouting commands, so Sherlock doesn't protest. "Look, why don't we try and get some rest and have at it again tomorrow. The new labs will be back, maybe that will give you a direction to look in, and if nothing else, we'll both be fresher. Okay?"
Sherlock agrees unhappily.
If it were just him, he could stay there for days without food or rest testing reactions and eliminating theories until it was solved, but working like this is exhausting for both of them, it slows his thinking to have to go through another person, to have to verbalise, he can't just connect and follow instinct, John is compliant but he can only be pushed so far, Sherlock's worn him out but there's no other way to do it…
They decide to walk home, even Sherlock agreeing the fresh air will do him good. To his mild surprise it's morning rush hour – they'd been in the lab all night. He's bad enough at keeping track of time, of days, during a case, but now he feels complete unharnessed from any sense of the world's rhythms, without even light cues to remind him what's passing.
Sherlock stays close to John in the busy street, holding John's belt under his coat in a way he hopes is unnoticeable to passersby. He had thought they'd be strolling deserted streets in the middle of the night and he could let his guard down, not jostled this way and that by unknown masses. Crowds are bad enough when he can see them coming but now he feels like he's being attacked from all sides.
Anyone could be around him, he'd never know, never see a man walking straight up to him with a knife, never know if Moriarty passed within inches from him, if John slipped away from him Sherlock might never find him again, he hates this train of thought but he feels the panic starting to rise again with thousands upon thousands of people surrounding him and no way to filter out what's going on…
Suddenly there a loud noise in his left ear and a spray of wetness on the side of his face. Already wired, Sherlock jumps practically out of his skin and turns to the source, ready to defend himself.
"Terribly sorry," a young man's scared voice mutters as it flees behind him. Someone had coughed on him while they were waiting at a street crossing. That's all it was.
"Christ," John says at his overreaction. "That's it. We're getting a taxi the rest of the way."
Sherlock doesn't bother to protest, letting John lead him to the kerb as he attempts to calm his heart, and wipe the phlegm and saliva off his skin. When they get home he goes straight into the shower, hoping to wash away the unpleasant sensation as well as the terror that had been clutching at him in the street.
He does feel calmer when he emerges, though still unsettled by how easily he had lost his equilibrium. John is concerned too, sitting beside him on the sofa and leaning into his side, the pressure of his body warm and reassuring.
"Sherlock," John says, squeezing Sherlock's thigh through the satin of his – he hopes – red dressing grown. "We're going to solve this. We are. I promise. But after today, we both know it might take a while. I think you need to figure out how to function… like this. Because you might have to."
Sherlock opens his mouth to lash out, but then shuts it. John's right, he realises. He can't be constantly on the edge of losing it. He's got to learn to work around this, he's got to find ways to be himself, to do what he needs to, without his vision. If only temporarily.
He nods silently, and John apparently sees what he needs to know that Sherlock's accepted what he's said. "I need sleep, I can't think straight. You should join me."
"Not yet," Sherlock says. He needs to think about this. "Soon."
John leaves him, reluctantly.
Can he still be Sherlock Holmes like this, maybe he can, as John showed him yesterday the loss of one sense is the heightening of others, there's nothing that can truly replace visual input, but he can sharpen his other senses, even in the crowd today, if he hadn't been so consumed by his own vulnerability, there were rhythms of footsteps around him, sounds of breathing, shifting, conversation to be aware of, smells of perfume and cologne and exhaust and food from shops, vibrations of the street, alternating warmth and coolness of shadows and light that could have told him as much about his surroundings as his sight could have had he bothered to tune into them, he just has to banish that amputated-limb feeling and engage his mind, he's a poor genius if he can't overrule his irrationality enough to use what he has…
Keeping his eyes closed, as that feels more natural, Sherlock takes himself back from the moment they left the hospital, retracing their journey on the street but this time paying attention to all the cues he'd ignored before. To his surprise, he finds he can draw up a mental picture of the path they took, the streets they'd crossed, even some of the people they'd walked by – a woman in heels pushing an infant in a pram, an Indian businessman on his mobile speaking angrily, a group of school children with two harried teachers and three – no four – parental chaperones on a field trip.
Sherlock feels himself relax, slowly. It was only the darkness in his own mind preventing him from observing. He had let it wrest control from him, but he wouldn't repeat that mistake. Satisfied and relieved he turns his attention back to the cat burglar case, and it's only a matter of minutes before the answer comes to him.
"John. John, wake up!" John grunts and pushes Sherlock away.
"What? I've only been sleeping… an hour? Bloody hell."
"I know why our thief is obsessed with the pictures!" Sherlock crows gleefully. "And how to trap him."
He feels John struggle into a sitting position. "If you must."
"He only steals the jewellery to pay the bills. He doesn't get a thrill from it, or from the break-in itself. That's where we've been wrong. That's just money, he can't be trapped by luring him with trinkets, however valuable. He's got self-control there. What thrills him is the pictures – he steals personal family photos that only have value to the owners. And only ones that don't have copies or negatives or exist in digital form. He gets off on stealing memories that can never be replaced."
Sherlock is aware of how smug he looks at the moment as John breathes, "That twisted bastard. You're right!"
"Of course I am," Sherlock informs him. "Now, call Lestrade and tell him all he has to do to catch him is to have someone with a collection of historical family photos advertise for help in digitizing their collection. Our thief won't be able to resist getting to them first!"
"Glad you're back to your old self," John mutters sarcastically, though his relief is palpable. "Now if I do this will you please let me get some rest? And get some yourself? I swear you're going to turn me nocturnal."
Sherlock agrees and once everything is settled with the Yard, willingly lies down with John. He drifts off much faster than he thought he could, untroubled by the bright light that must be filtering through the curtains.
He's not sure how much later he wakes, but John's no longer beside him. He shakes off the disorientating darkness more quickly this time, but something else is wrong. He can't quite pinpoint it, so he calls out to John.
No sound comes out of his mouth. He tries again, but nothing. There is only silence. Not just from himself, but from everything around him.
He's being suffocated, being drowned, darkness and silence, is he dead, is this hell, he can move but he can't speak, can't hear, can't see, it feels like a vacuum, there's not enough air…
Sherlock fumbles blindly around him, feeling like the world is spinning, like he's plunging into an unseen abyss. He falls to the hard floor, hitting it with his knees, dizzy and still screaming soundlessly for John.