Sherlock flicked at the tails of John's bathrobe with the handle of his disused cane. It flipped up bare-thigh-high. No tattoos there. Pity.

John kicked at the shaft from where he sat watching telly. "Boundaries, Sherlock!"

Sherlock rolled his eyes, sick to death of the word and the meaning. 'Keep out, keep out,' always with 'keep out.' "Why do boundaries exist other than to separate people from what they might actually care to see?"

"It may shock you to know they aren't supposed to go both ways. They don't exist for the intruder; they exist for the person wishing to keep others away." And wasn't that the crux of it?

"Then, why do you keep invoking them against me?"

John's jaw fairly thunked with the force of his repressed indignation. As if he's got any right to be indignant. Sherlock threw his cane across the floor, pulling his legs up to perch upon the chair. What he'd seen wasn't enough, what he had wasn't enough. The entire ruse was making him snappish.

"Time and again, John, you've proven to trust me above all others. Yet, not with this, why not with this?"

It had been weeks and week since the clinic. Cases had come fast and furious in the interim, but they had gone to ground now, save the odd domestic discontent and studies in paranoia. Good money, perhaps, but they left his mind to rot.

"Leave off that privacy carp, it's old hat by now. We live in each others' back pockets and you've never had a single complaint. Well, save for the eleven separate occasions I've caught you engaging with those videos. Really, John, there's better pornography to be found on the internet. Surely, you must have come upon it by now." He paused. "Pun unintended."

John positively grumbled in his fluster. "All right, all right, you've made your point. Let's agree never to discuss that again." He raised his hand before Sherlock could go on to do just that. "Besides, if anything, those are perfect examples of why you should knock before entering a private room."

"But it isn't private, it's yours. Any other time, you'd never have asked that I announce my presence before entering a room."

"Because I know you won't."

"Which casts your complaints in a rather academic light, doesn't it? You know I'll continuously fail to comply, yet you consider it necessary to lodge your protests at volume for the sheer hell of it. Why?"

"You'll never learn if no one complains."

"Why should I learn? There's no one to care but you and it isn't as though you'll ever leave me because of it."

"You say that like it's a sure thing."

"I say it that way because it is."

John began to sport that unhappy, hunted look he had at the start. Sherlock didn't want him spooked, he wanted him laid open. He couldn't understand him any other way.

"Look, I get that you're interested. I'm even sort of happy you are. But, Sherlock, my skin is my business, like I've told you before."

"Why can't it be mine as well?"

"Why would you want it to be?"

Sherlock waffled. "Isn't that what partners do? Share business and secrets? You and I, we already solve cases together. We live together. On any given night, we might even fall asleep together. Why is this different?" Sherlock had pored over what all he'd seen of John, but that was like a case with only half the evidence in sight: he couldn't work this way. And I want to know, I want to understand. John seemed to be the only one not to recognize that for the feat it was.

"Because I'm me and you're you, and it just is."

"That isn't any kind of answer. It doesn't even make sense! Look." Sherlock shoved off his sleeping gown and yanked his t-shirt over his head. He left them in a pile on the floor. He twisted to point over his shoulder, offering John a generous view of his spine. "See that. I've got an arc of acid burns across my back from a decathlon-runner turned research scientist in Cardiff. He didn't care for my interest in his work."

John's wariness didn't abate. "He went to prison for that, I hope."

"Fell from a pier." Pushed, but who was to know?

"Just as well."

Sherlock slumped in his chair and set his feet on the nearer armrest of John's chair, giving his toes a tentative wiggle. "I lost sensation in the tips of my toes from frostbite. I was apparently the only imbecile outside during the worst winter storm in Sussex history."

"That should shock me more than it does."

"Not necessarily. Even geniuses play long odds. I count myself lucky to have retained full use of my fingers at the very least." He wiggled those as well before curling each finger in turn. It was difficult for him to fathom that he'd come so close to never playing the violin again. Years of dissonant and melodious joy dashed on a whim. He preferred not to think about it.

In spite of John's pretended lack of interest, he blatantly examined the proffered digits with a clinical eye. "We'll have to keep you in leather gloves, then."

"Precisely."

"And socks." John dragged a knuckle along Sherlock's left instep; his foot spasmed and his abdominal muscles flexed in what might have been a laugh had Sherlock not stifled it. He hadn't been ticklish since the age of five. He wasn't intending to start that up again.

"Most definitely," Sherlock coughed, wilfully disregarding the self-satisfaction he read in the wrinkles outside John's eyes.

He rucked up the right leg of his pyjama bottoms, ready to get on with the thing. "There's a similar mark here on my calf." The elongated patch of skin was discoloured and satiny in texture. Only luck and the benefit of modern medical technology had prevented gangrene setting in. "Most mistake it for another instance of frostbite and, after a fashion, they wouldn't be wrong: an experiment with card ice gone slipshod. A fragment of the lot I was working on got away from me and sublimated while I was manipulating the larger portion. The gas reached my lower extremities first. Had I not felt the cold, frostbite would have been the least of my concerns."

"You'd have asphyxiated."

"It wouldn't have been pleasant. I've since learned to take more care with my safety measures."

"Severed heads in the fridge is you taking more care?"

"No backchat! I like to think I came out all right, given the alternative."

John laid his hand over the scar; it exceeded his hand for length. "Can't say I disagree with that."

Sherlock basked in his momentary amity. John could be interesting, he could be the most interesting person in the room when he deemed Sherlock worthy to be entertained.

John elbowed Sherlock's foot from his chair. Sherlock glared, unappreciative of his rough handling. "Not that you're doing much to hide it, but I do recognize what you're doing, Sherlock. And, while I appreciate the effort you're going to, I can tell you it won't work."

"What won't work?"

"You trying to get me to show you the rest. You can't force a confidence like this, mate, however harmlessly-meant. I'll show you someday, I promise I will. I'm just not there, not today. Sorry." John's solemn-eyed sincerity would have been appalling on anyone else.

"It's fine." John hadn't ever shared a league with anyone else, nor would Sherlock have meant his words for another's ears.

The sway of John's lips was as true in resignation as in good humour. "I wish I could believe you meant that." He knows me too well. Sherlock didn't like to be doubted, even with good cause, and by John least of all.

"So do I."

...

Sherlock could have throttled himself later for not more effectively skewering John's doubts at the source.

Recent days had seen John lapsing into introspection for hours at a stretch, his gaze set on crap telly for the duration without a sign of laughter. He would rub at his forearm tattoo—the new one, the one to which Sherlock wasn't yet privy—in fervent contemplation. Like an adherent to an icon. Sherlock hadn't meant to wake a sleeping a beast, he'd wanted to lay John's hands to a stop but hadn't dared. Hadn't he done enough to disturb his friend's fragile balance? In his own tedious insistence, Sherlock forgot that for all his bravery, John had yet to step down from his tightrope walk. And as unerringly as Sherlock had saved his life, he might unknowingly induce its end. I can't be trusted with him. Why was I entrusted with him? Sherlock was wrong-footed here. What if London's heart no longer beat for him?

Sherlock stepped from out of 221 with every intention and nowhere to go. It was mid-evening and the spring showers were out in force, painting the sidewalks, cars, and streets in oil slicks and muddy refuse. There was every vapid soul in sight save for the one Sherlock wanted.

"John! John..." He couldn't see John for the dark and the rain, couldn't have seen him on a bright day as he wasn't there to be seen. "Shit." Naturally, his flatmate would learn the proper way to duck pursuit on a night when Sherlock needed to find him. He pulled out his mobile, intending to text the man to return home at once when he remembered that John had left his phone in the sitting room to charge alongside his laptop. "Wonderful, exactly what I need."

Sherlock cast about his mental map of the area to deduce where John would retreat to half-dressed in the rain as anything other than a last resort. After the way his relationship had ended with Sarah Sawyer, he'd not risk inconveniencing her now. John hadn't taken his wallet, so no pocket change. Anywhere he went he'd have to go on foot. There was nowhere in walking distance that he might go save back to the flat. Sherlock was free to wait for his return. But he didn't wait.

The rain was pelting down, the chill of the air was creeping into Sherlock's limbs despite his coat, scarf, and gloves. John had none of these, in fact, he had much less and given his mood he might sulk for hours out of stubborn pride. Or hurt. Sherlock hadn't intended to hurt him. He recognized that he could be impatient and entitled and petty on the matter of John's secrets, but this once he'd only been oblivious.

He'd stolen into the bathroom while John was brushing his teeth after his evening shower. He hadn't clapped eyes on the man so focused was he on what he'd planned to share. Sherlock hardly remembered what he'd wanted to say anymore. All that came to mind was John's face, how his eyes had positively burned as he'd turned and marched out of the flat in house shoes, sleep pants, and a thin shirt. John hadn't ever looked at him that way. He hoped to make it the last time.

The harsh rain softened to a drizzle though it did nothing to lessen the bite of the wind. Sherlock turned up his collar against the invading mist and set out to find his friend. Speedy's was a clear miss. Too close. He wouldn't risk me finding him. Angelo's was the wrong sort of place for John given the hour despite the fact that the restaurant owner could have easily allowed John use of his private office to cool down. Too far and John would be mortified to be seen less than decently dressed by the regular wait staff. John wouldn't have been able to board a bus or hail a taxi, leaving Sherlock with his best guess and not much else.

Public place, free of cost, low probability of being disturbed. Close proximity to home. His leg would have bothered him. Emotionalism, Sherlock abhorred it; nevertheless, he acknowledged John wasn't built as he was. Inadvertent slights had the capacity to rip open nonexistent wounds. Someplace open but secure. Someplace he would have felt least threatened.

Sherlock swore at his own stupidity. It was obvious. John's emotional, he doesn't think well when he's angry. He would have gone to the Tube Station after realizing he couldn't visit Sarah. He would have arrived only to realize he'd walked out without either cash or Oyster card. And he would have stayed rather than face me right away.

Sherlock forewent a cab ride altogether to make shorter work of the trip on foot. The weather wasn't a deterrent to criminals and he'd hate to have to bail John out of lockup in the mood he was in.

Upon arriving, he managed to get a third of the way down the staircase before he spotted John. He was huddled on a bench under a triptych of Doctor Who advertisements, more half-frozen than still fuming. Not that that'll stop him laying me flat his first chance. The platform was hardly bare, but Sherlock deduced that none were likely to alert the authorities in the event of a confrontation, so there was some good to be found in that. However, any notion of bracing himself for a fall passed as he finally got a look at what he'd supposedly already contrived to see.

Christ.

The rain had effectively rendered John's vest transparent and left it clinging. The unsuitable cast of the overhead light be damned, John was remarkable. The Kandahar-London map ran up the length of his right arm, from wrist to shoulder, seamlessly absorbing the RAMC cap badge that he wore with pride. On the opposite side, a green and gunmetal serpent coiled downward toward his forearm, great mouth open to disgorge...a bomb. Why the serpent, he queried to himself, but it couldn't hold sway over this new data; it was devoured by it.

It was a bomb, one Sherlock could have identified with one eye and his memory shot. It was an adaptation of the vest Moriarty had strapped John into that night at the pool, bar one crucial feature. Sherlock couldn't be sure—and Sherlock was always certain—but he thought the arrangement of the wires that had coiled amid the Semtex was wrong. It nearly gleamed and lay in four parallel lines as the wire hadn't in a formation Sherlock would know to recognize before the spelling of his own name. I had no idea John was so enamoured of my playing. The knowledge sat like bad a meal, like infatuation.

This was the symbol John had painstakingly cared for over these several weeks. Sherlock couldn't begin to deduce his motive for that.

John looked up from his vigil over the detritus littering the platform floor and, if possible, drew himself tighter, lower once Sherlock met his eyes. In trying to make himself disappear, he made himself all the more visible. For want of a better course of action, Sherlock continued his approach. He continued his approach even as he spied the rest and words failed him.

Featured in muted, enduring colour across the expanse of John's hunched back were lungs. Faultless imitations of the organs, no surrealist dream, blooming a robust red-pink with ripe blood vessels running hither and yon the thoracic region through. The image of them positively bled through the fabric of his shirt in grotesque pageantry. They heaved to his every shudder; they were alive as he was.

This explains everything. Somehow. Sherlock would retreat to his Mind Palace to sort the lot at a later time. Just now, he needed John.

"This is why. The jumpers, all the layers, the buttons, the undershirts. This is why bother despite how difficult they can be to remove at the end of the day." Sherlock sat down at John's side, straining to catch his eye. "They're remarkable. You shouldn't hide them." You shouldn't hide you. He felt the fool for ever thinking John the dull one.

"It's not a modesty thing, it's just," John exhaled shakily. "God, you'll hate it. You'll hate it. It's sentiment through and through." He clenched his red-rimmed eyes shut. "We give everything we are to every person we meet. We shake hands, we say our names, our occupations; if we're Sherlock Holmes, we open our homes. There's nothing left for ourselves but the skin we're born in." He rubbed his intolerably bare arms; Sherlock's fingers flexed for want to shelter them. "This is mine. It isn't much, it's got dozens of scars, but it's mine. And I thought if I just made it something worth seeing..."

Sherlock considered the plethora of stories encompassed in such a statement and discovered something far beyond his comprehension taking root in the empirically nebulous 'place within': something quite like tenderness.

"It is worth seeing, John. As you are." Sherlock could have shaken him as soon as shown him a mirror. There was nothing 'unworthy' about John, or his ink totems. Their left and right bronchi were lushly depicted, narrowing artfully into bronchioles and alveoli in the lower lobes of John's ersatz lungs. Sherlock wanted to touch, but his fingers refused the contact. The drawn lungs seemed to fill and deflate as real lungs might, powerful and wretched across his flatmate's back. For all that he'd imagined insipid wings, these were beyond imagining.

"Why?" The word was far too small to contain the methods and means by which Sherlock wondered.

John remained curled over himself, shuddering for cold and anger and unbearable weariness. "Because, sometimes, I can't breathe. Not since Afghanistan, not since coming back. Thought if I had another set of lungs, they might help."

"Do they?"

"Not every day but some days, they're the only thing..." John's shivering grew increasingly violent till he tucked his hands against his ribcage to quell it. "God, I'm barely even dressed. What's the matter with me?"

Sherlock thought, Nothing at all. He asked instead,"Can I do anything?" Sherlock would breathe for John, would fight for John and, possibly even beg. It would be less than the absolute least he could do to keep him warm.

"I'm all right."

"You're shivering, but only just so, which indicates that your core temperature may be dropping to a dangerous level, potentially even hypothermic. Don't be stupid, John. Being right isn't worth the risk to your good health." Hysterical nonsense. I'm being hysterical. I am not hysterical! He took a mental step back. Am I? He couldn't answer.

"That's a bit rich coming from you, isn't it?"

Sherlock gave himself a reaffirming shake. "I've never claimed to be free of hypocrisy. No one is."

"Too right." John's breath rattled in time to his response.

John was ill, obviously ill and Sherlock hated to see it knowing that it was partially his initial prying that put John there. In a fit of inspiration—he'd seen something like it on late night telly—Sherlock shed his coat and draped it over John's shoulders. That fit was doubtless a touch narrow, but the wool would do him well.

"Let's go home."

John gave a nod and tried to stand. His weaker leg folded the instant it took his weight, leaving Sherlock to snatch him up from a regrettable spill.

"All right?"

"Shoulder hates the cold; leg hates it more and has veto power. I'm as good as I can be."

Sherlock hooked his waist to start a slothful tread. "Grab hold of me. I'll get us home."

"I know you will, I trust you."

"After all this?"

John tipped his head in deference to a shrug, stifling a groan of pain as he hobbled. "When a sociopath comes out in the rain for you it's usually a sign that he gives a damn."

Sherlock hadn't considered his actions in that light. He hadn't considered them at all, really, rather the potential outcomes that would result if he left his friend to stew in his upset as he tended to do. I suppose this is what it means to care.

"Don't be fooled. I only came at all because I was in need of tea and there was no one there to make it." That wasn't entirely untruthful, Sherlock had never longed more fervently for a cuppa.

"Likely story," John groused in good-natured scepticism as they ascended the stairs at a slow clip.

Sherlock slackened his lengthier, swifter stride to accommodate John's spasmodic limb, sparing the flintiest possible gaze for any passerby who might conceivably try rushing him aside. John was oblivious as always, but he held on at Sherlock's waist just as tight. So much for what people say.

Sherlock may have become infected with Molly Hooper's brand of disquieting optimism, but he thought he might have this caring lark figured out yet.