1: Deduction

John has short legs. That's just a cold fact. He's small for a man and he has short legs. When he's walking with some tall, energetic type—not that anyone particular comes to mind—it takes a pace and a half on John's legs for every one taken by the infuriatingly longer-legged hypothetical person. He suspects the effect is very similar to watching a terrier trot to keep up with its human.

Ironically, this is much like how John feels when Sherlock is thinking near him, only on that front, he's thrown in the towel on the 'keeping up' part.

Case in point.

"The painting, John! Oh, I'm so blind! Someone switched the painting out!" Sherlock hits himself in the forehead with a closed fist to hammer home the memory of this day when Sherlock Holmes fell to irretrievable stupidity, then his voice sinks down to a mutter. John catches snatches about faded paint, the sister's attempts at comfort, and the lawyer's hidden affair. Apparently it logically follows from all this that the rubies may be found somewhere on the left side of the garden shed.

Well, obviously. How could you have been so ignorant, Sherlock? John doesn't say, because he would not be thanked for interrupting a moment of epiphany with vacuous sarcasm.

He doesn't have time anyway, because an instant later Sherlock is off and running, John dogging his heels because, he'll assume till he gets a chance to ask, his flatmate has probably just figured out where the bodies are buried.

John can't hope to keep up with this. It's like racing a whirlwind. He can chase it all he likes, but he can never catch it, and there's always a threat of it tearing him apart if he gets too close. But, hell, he loves running, and life without risk is an ugly, drab thing, so he chases the storm that is Sherlock.

2: Boredom

The problem with having a cyclone for a brain, John reckons, is that the traditional purpose of a cyclone is to tear things apart.

Sherlock is decked out in his dressing gown and his rattiest grey tee shirt—John hadn't even known he owned a ratty tee shirt—and has coiled himself into a huffing, brooding ball on the sofa. He is a ball made of brood. Brood is getting everywhere; it's probably sinking through the floor down into Mrs. Hudson's rooms. John considers going outside just to see whether he can catch it wafting up and down Baker Street.

It should be funny—and okay, Sherlock sulking is a little bit funny—but really it's not. Because Sherlock isn't just miserable when he's like this; he's in pain. It's not a physical pain, but that only makes it worse. Can't take two paracetamol and call the doctor in the morning to make this go away. Not even if that doctor is John.

He can't help, and it kills him.

The thing is, John is not wholly ignorant of what it's like to have his own mind turn on him with fangs and claws. If you want psychological stressors, let's talk about months of depression and rehabilitation after nearly having your shoulder ripped off by an enemy marksman. He knows what it is to be cannibalized by his own head.

But this… This thing that happens to Sherlock when he doesn't have some other prey to feed that ravening monster he calls a brain? It looks like a form of insanity, but if so, it's not one they have treatments for. John isn't surprised that Sherlock's tried drugs, something a damn sight stronger than paracetamol, though frankly he's at a loss as to how they would help, other than by sedating the offending intellect into oblivion. And that, thankfully, Sherlock is not interested in.

He can't quite work out what Sherlock is after, come to that; whether he craves for stimulation, or distraction, whether he's bored because the world is dull and flat without the high of a case, or because when he's not on a case, he thinks about other things he'd prefer not to. Both? Neither? John doesn't know how things work up there.

But hand to God, there are days when he's half-tempted to find someone he can murder interestingly in order to make this stop.

3: Music

Sometimes Sherlock plays the violin beautifully. More often, it's a tool to give voice to all the things in his head that English fails to contain.

Occasionally, he becomes the violin.

Like right now. Sherlock's world has ceased to extend beyond the graceful swoops of wood and bow. The sounds—not music, he stopped playing music some time ago and is now on to raw emotive soundscapes—lap and swirl around the room until maybe John can't see the spiralling gales of his friend's mind, but he can certainly hear them.

It's still beyond him.

Sherlock plays the violin like it's his own wood-chambered voice box. John listens silently from a kitchen chair that he dares not rise from for fear the scratch of legs on the tile will break this trance. He fancies he can hear maths in the noise; wild fractal patterns of repeating rhythm and tone curling in and out of snarls and sobs and chortles of expression, spattering and shifting as, he imagines, Sherlock chases down all the various outcomes to some problem that's haunting him, one iteration at a time.

It leaves John feeling unutterably sad. He feels terribly alone, and he can't tell, submerged as he is in the contents of his friend's thoughts, whether it's Sherlock's aloneness, because he reaches so far beyond all the rest of them that no one can ever see what he sees, or if it's his own, because he's the one left behind.

4: Morality

Sherlock is not a sociopath. John knows this because he has personally seen the man make selfless overtures of friendship toward Mrs. Hudson and risk his life for John himself.

But there are days when he wonders whether too much reason can be a form of insanity.

"Mr. Spock was capable of displaying compassion, you know," he says disapprovingly after Sherlock makes their witness cry. She wasn't even a suspect. She wasn't even an adult. He made a teenaged girl cry. On purpose.

"Hm?" Which is, John knows, code for Not right now, John, I'm thinking.

But oh yes. Oh yes, very much right now.

"Compassion," he snaps. "Mr. Spock? Don't tell me you've never seen Star Trek, you must have done. If any man was ever born to be a Vulcan, it's you." The pop culture reference is deliberate, because John knows it will annoy Sherlock, and annoying Sherlock will get his attention, whether he wants to give it or not.

He doesn't wait for Sherlock to respond. The minute those storm-lit eyes focus on him, John presses, "You just described to that poor girl in painfully accurate detail how her mother died. That does things to people, Sherlock. You may have just done serious damage to that child, and that is very far from alright. So I would really like an answer, right now, as to what could possibly justify that, or I am going to talk to Mrs. Hudson about getting the locks changed and you'll be sleeping on the stoop for the next fortnight."

Sherlock opens his mouth, and John knows, knows that what's about to come out will pertain to the futility of locking him out of any building he wants to get into. John's glare ratchets up another notch to somewhere in the vicinity of promising bodily harm, and Sherlock wisely chooses to answer the stated question instead.

"I'm 75% certain it's her uncle."

"But her uncle is-"

"Her guardian, yes. She trusts him, so she'll talk to him, seek comfort, tell him what I told her. If I'm right, he'll panic. Most likely he'll target me, fearing that he's been uncovered, in which case you and I will be ready for him and we'll have all this wrapped up within 36 hours."

"Oh my god, Sherlock!" He reaches out to grab the other man's arm and jolt him to a halt. He hadn't thought Sherlock could actually make this worse. "If her guardian's the one who did this, then what kind of danger did you just put her in?"

"I lessened it!" Sherlock glares at him, offended. It's something of a relief, actually, to see that he's angry at the accusation he would willingly put a child in harm's way. It's comforting to know he's got standards. "If it's her uncle, and as I said I'm 75% certain it is, she would be his next logical victim. But if he believes we're onto him, he'll put that off and come after us instead. Now you have a gun, military training, and a general enthusiasm for putting yourself at risk. If you would rather I avoid interfering in the natural order of things…"

"No. No." John holds up a hand defensively, then rubs at his forehead. He suddenly feels exhausted. "No, look, I'm sorry. I… If that's how it had to go down, then you're right. It's better than the alternative."

Sherlock nods once, sharply. The next time he's sure no one is looking, he slips John's gun from his own pocket into John's windbreaker and pats him reassuringly on the shoulder.

John watches him walk away, trying to decide whether this feeling knotting him up is horror or pride. He will never understand Sherlock Holmes.

+1: War

Sherlock has, he'll tell you if you ask, an exceptional imagination. In point of fact, there's precious little he can't imagine if he puts his mind to it. This ability is one of his most powerful tools, enabling him to accurately model scenarios in his head and logically extrapolate events. He might even go so far as to say it's at the core of what he does.

So it's understandably frustrating, he believes, to find himself coming up against his limits when it comes to John Watson.

John and his damned nightmares.

Sherlock would agree to substitute teach Introductory Chemistry for a pack of Liberal Arts undergraduates before he'd admit this aloud, but John's nightmares alarm him. It's not that they're violent; quite the opposite, in fact. John doesn't cry out or talk or toss and turn when he's having a nightmare. But between their shared living space and the acrobatic schedules they keep on cases, Sherlock has seen John sleep any number of times, and it's no great effort to spot the bad nights. Normally John is much the same at rest as he is awake: open, honest, and warm. He has good dreams and bad dreams, happy and sad and angry ones, and each is written on his body for anyone with the eyes to see. But when he's having one of thosedreams, he goes…stoic. As though there is no hope, no possible resistance, nothing to do but endure whatever it is he's living through on the other side of sleep.

If there's anything in the world Sherlock needs to understand, it's what could be bad enough to break a man like John. Not that John is broken now. Sherlock fixed him—and he did a bang-up job, if he does say so himself. But the implications remain disturbing, as is that barren, abandoned look that comes into John's eyes every now and then, when the memories catch him in waking moments. John feels far out of reach at those moments, and Sherlock feels very alone, which he never has done in his life.

So he works to imagine war. Sometimes, he's convinced he's got it. He has, after all, seen more than his fair share of blood, death, gore, victimization, violence, guns, bombings, chaos, and general mayhem. He has built model after model in his mind, of battlefields, ambushes, military bases, medical emergencies. He's taken into account the endless, grinding demands on a surgeon in a war zone, the whiplash effect between long stretches of dust and boredom interspersed with sudden, unpredictable violence, and the stress of dealing with enemies hidden among the very local populations meant to be safeguarded. He's considered—it came with startling ease—the unique bonds that form between soldiers in battle, isolated from normal life and in danger with no one to rely on but one another, and how it must feel to lose those brothers in arms. He's even imagined the pain a man with John's unflinching morality must feel when faced with the paradoxical need to kill to protect.

But all he can imagine, even accounting for the multiple types of trauma involved in the wounds John took, doesn't seem like enough to put that look on John's face.

Moriarty came nowhere near it. Being strapped into a semtex vest and held hostage by an evil mastermind only served to frustrate and provoke him. Sherlock is forced to concede the possibility that there are elements to this he simply doesn't have the data to quantify. It's the essential shortcoming of the beast, isn't it. You can't imagine what you can't imagine. And he further finds himself not only taxed, but close on unwilling to imagine what could make John give up.