In which Sherlock is moping, Severus is morbidly curious, and John inadvertently introduces the two least pleasant men he knows.

A/N: This little story of mine is based off The Jumper Chronicles by HermioneGirl96. For the most part it can stand alone; I think I do a pretty thorough job of explaining most of the background I reference, but if nothing else I recommend that you read ch. 27 (The Boggart), for an excellent scene referenced herein. This adheres pretty well to the (hitherto revealed, through the 43rd chapter) TJC plotline. Mycroft's altered role, the delayed return of Sherlock and John to Scotland Yard, future plot twists, and any other deviations for my own purposes are explained. Intended as a one-shot.

This whole thing was pretty much an excuse to write Sherlock and Snape being bros. Apologies for incidental angst.

John edged into the empty office, trying not to let himself dwell on the possibility that Sherlock was going to despise him for this. The odds seemed very good indeed.

It had taken him a long time—probably much longer than friendship dictated, but in all fairness Sherlock had put him through a lot lately—to come to the conclusion that Sherlock was right. About…well, any number of things, really, but it was a specific conversation that kept replaying in his mind. One they'd had long ago, and that he'd brushed off as simply another manifestation of Sherlock's usual melodramatic tendencies.

John, I envy you so much.

John had almost laughed aloud at that. You envy me. Right. Funny little brain, remember?

My mind is like a rocket, racing out of control, tearing itself to pieces…

Then you ought to be able to empathize with the current state of the flat, John had barely refrained from replying.

I need a case!

Half a demolished living room, a pack of discarded cigarettes, and the footprints of a gigantic hound later, they'd had one. John had spent the rest of the afternoon shaking his head at the speed with which Sherlock's manic desperation had dissipated into barely-contained glee.

And if he hadn't realized then, John's only defense could be that people rarely said need and meant it. Or perhaps he was simply jaded—heaven knew, as a doctor, he'd dealt with far too many of them. Too many patients needing an obscure vaccine or procedure and it was all he could do to hold back a no, stop, shut up and listen to someone who's actually been to medical school…

Google University was a bloody menace, in his mind.

Not that Sherlock would in a million years resemble an overanxious or even mildly conscientious patient. No, more like the complete opposite (and that had its own part to play in the current debacle). But there were other examples too. Harriet and her ever-present need for alcohol swam into his mind…but no, that was hardly a fair comparison either. Similar in its own way, but how could he complain, when Sherlock's addiction saved lives?

And it wasn't as though John himself were free of that particular dependence either—with a downward glance at his perfectly steady hand.

No, it wasn't the cases that drove them both mad. It was the lack of them. Occupational hazard of being officially deceased, John had commented dryly to Sherlock, earning himself a mute glare from the sofa. Perhaps the triumphant return had been a bit less sensational than Sherlock envisioned. He'd been all fired up to stroll back into Lestrade's office the very next morning…but the timely arrival of his brother had put a stop to that. The elder Holmes had urged caution until his own network had finished the sweep for loose ends, pointing out that there was still potential for everything to end in tears. All it would take was one lingering gunman, one bullet. In the end even Sherlock had the sense not to argue with that, though after the past year John suspected the forced inactivity was killing him.

Still, he hadn't expected his flatmate to crack quite so soon.

Should have known better by now.

The most recent 'case' had taken Sherlock nearly ten months on his own. John's belated return for the final few months had expedited the process considerably. And now, a year later, they were back where they had started. Baker Street. Still barely a week since they'd tied up the last of the web.

Well… 'tied up' was something of a euphemism. And maybe that was part of the problem, too.

I've spent the past year killing people, John, not playing nice.

That had brought John up a bit short. Certainly any action against Moriarty's network had been justified, but put that way…

And one more, simple admission.

I'd never killed anyone before I left.

This was where John had frozen, unsure how to read the look in Sherlock's eyes, what to say. Embarrassed to admit the thought had never quite occurred to him. It was…well. Astonishing enough in and of itself, given the man's career choice, but it was the verbal concession that sent up a huge red flag. Especially given that it followed months and months of methodical (and generally messy) dismantling of Moriarty's network, during all of which Sherlock had displayed no more sensitivity than a computer mainframe carrying out a particularly sophisticated program. But then, he'd always been able to do that, hadn't he, when the mission required it.

Swapping metaphors, if John thought he'd witnessed the rocket tearing itself to pieces before… well. Looking back, it hadn't even left the launchpad.

Just as Sherlock hadn't bothered to pry himself from his long-neglected mattress in two days.

I need a case, indeed. John was pretty certain he could think of any number of healthier solutions, but where Sherlock was involved almost every traditional outlet ceased to be an option. Still, he had a feeling it wasn't a case his flatmate needed so much as a distraction.

And those were not forthcoming. Unless you counted Mrs. Hudson's twittering.

What he didn't want to admit, what it came right down to, was that John blamed himself. If the past two months had been ugly, he didn't even like to imagine what Sherlock had been through on his own, the previous ten. With no magic of his own, he'd have been entirely at the mercy of fate, his own wit, and whatever resources Mycroft could provide. In constant danger that John shuddered to imagine. And all this while Sherlock had actually left the key to his clandestine survival right on the bloody coffee table.

Surely some sort of tribute to his dead friend should have sent John back to Baker Street for a few days, if only to recall the good moments in a life that ended in the worst possible way…but no, he'd been paralyzed by grief. Had barely set foot back in the flat, just grabbed a few things and left. Weak, it seemed now—but it wasn't his fault, was it, that the déjà vu of one location was suddenly worse than the other?

So it was back to the only other place he'd ever called home. And John—well, Remus—had done some good at Hogwarts, hadn't he? Been a teacher, a friend even, to James' son. John had never fancied himself a parent figure (well, except on days when Sherlock was acting particularly childish), but it was gratifying to know he'd been a good enough teacher that Harry had sought him out for help with the Patronus charm. Shared some of his memories, even. It had made an odd sort of contentment swell in John's chest; Merlin knew the boy had few enough trusted adults in his life.

And John had accomplished one more thing, even more important, in deducing Sirius' innocence. Even Sherlock had been approving when he related the tale, though he'd been distinctly less impressed when John admitted his neglect in overlooking the Wolfsbane Potion.

But even if Peter had escaped, even if Sirius' name wasn't cleared, at least he was free—free with his disguise intact, with transportation, the ability to communicate with his friends, and the promise John had exacted from Dumbledore to provide him with a wand, as soon as possible… John had already determined to go and see him, as soon as his friend settled down someplace relatively safe.

What a relief to think of him as Sirius, again, instead of Black. An even greater relief to know that the two closest friends he'd ever had hadn't truly betrayed him in their own different ways.

But Sherlock's current behavior was a very unwelcome reminder of why that betrayal had been plausible in the first place.

Dumbledore wasn't there.

John groaned silently, weighed the likelihood of Sherlock noticing a prolonged absence against the sound he would probably make rematerializing in the living room fireplace, and decided to take a chair and hope the headmaster wouldn't be long. There was really no way to know; it wasn't like he'd made an appointment. That would require forethought, and this was more a spur-of-the-moment thing.

John glanced down at the plush, gold-edged carpet before lifting a foot out of the grate. Dumbledore had left him with a standing invitation to visit anytime, even linking Hogwarts and Baker Street via the Floo Network. For some reason, however, the ornate office still brought back vivid memories of John's Marauder days. You would think after teaching here for an entire year he would feel a bit less like a wayward student ...John shook his head. Best not to track ash all over the carpet, regardless.

And so he was too busy trying to bring to mind the spell that would siphon the ash from his shoes to notice the door creak open. Silently.

How a door could creak silently John didn't know, but in retrospect only one person could have managed it. It was a bit embarrassing how far he jumped when he finally raised his head and caught sight of the intruder. Snape smirked.

"Evening, Lupin. Or shall I say Watson, now?"

The greeting was toxic, as usual, but John kept his own reply as blithe as he could. "Severus."

Shoulder-length, limp black hair framed a familiar sneer.

"To what do we owe the, ah…repeated pleasure?"

"I need to talk to Dumbledore," John said shortly.

"Regarding what? Has your old friend Black finally found himself a Muggle hidey-hole? Next door to your own, perhaps?"

John blinked, and then, to his own surprise, choked out a hoarse laugh. Despite the incendiary tone—and the not-so-distant memory of Snape doing his best to turn both John and Sirius over to the dementors—the thought had briefly flashed through his mind that Mrs. Hudson did have another flat to let.

Merlin, no. The thought of Sherlock Holmes and Sirius Black in the same building was too much.

Severus' expression hardened as his coal-black eyes scanned John's, obviously uncertain how to interpret the laugh. John chalked that up as a small victory. He'd have liked to say he had nothing against Snape personally—certainly he understood, better than anyone, the man's lifelong enmity toward Sirius and James—but given recent events…well. Impossible to pretend anything beyond sheer bitterness had prompted Severus' 'accidental' revelation to the Minister of Magic. But personal motives for driving the last Marauder from Hogwarts didn't alter the fact that for John it was yet another lycanthrophobia-spurred step toward total rejection from the Wizarding world.

But then again, if he hadn't…

That file—all angles, trajectories, airbags, blueprints—might still be lying untouched on a coffee table in an empty flat. John would still be employed, semi-content, and grieving. Sherlock might still be wandering the Middle East.

Or dead.

So John was ignoring the more-or-less open warfare of the past school year in favor of neutrality. Which, admittedly, grew harder with every word from the greasy git's—er, highly competent Potions professor's—mouth.

"No," he said mildly. "I've no idea where Sirius is. When will Dumbledore be back?"

"Another day at least. You know how things are at the Ministry these days…" with the air of one discussing a change in the weather. "All those escaped convicts roaming about—"

Another day. John's heart sank. It was too much to hope that Severus would take a message. Perhaps he should get an owl, though Merlin knew how long it would take one to navigate the labyrinth of the Ministry.

May as well try, anyway.

"Would you let the headmaster know I need to see him at his earliest convenience?"

"Shall I invent any sort of motive for your intrusion into his office, or would you prefer to offer your own?"

Curse him. "It's about a potion. That's all."

John turned to go. Severus' silky voice stopped him.

"If you're expecting the headmaster to continue furnishing you with Wolfsbane Potion, I'd hardly call it a pressing matter."

John actually swung around at that, bristling. "Of course I'm bloody not. Though money is a bit tight these days," he added pointedly, watching the expected sneer unfurl on Snape's face. "No, it's something for a friend. And rather urgent too. So if you'd pass on the message…"

The Potions professor heaved a sigh, making no effort to conceal his irritation. "In that case you'll save time by relating the relevant details now."

With these words he dropped into a chair, and when John made no move to do the same, raised an eyebrow.

"Come, Lupin, don't tell me you hadn't thought as far as to whom our venerable headmaster will delegate your urgent task."

There was more than a little bitterness in the tone, and John felt a frown crease his brow, because in all honesty, he hadn't. The realization made coming here seem even more of a bad idea.

There was always the alternative of doing nothing, which was precisely what his own attempts at distraction had amounted to. Not that Sherlock wasn't interested in magic, of course, but he'd quickly grown impatient with John's floundering attempts to explain what he really wanted to know: the fundamentals of magical theory. During the past few months he'd grown well enough acquainted with the effects of transfiguration and defensive charms that the first keen edge of investigation had worn off. In his current mood, at least. Until Sherlock thought up some new, mad experiment involving something besides the relative decomposition rate of magically transfigured corpses (which John adamantly refused to provide) there wasn't much John could do. He supposed he could Apparate them somewhere obscure; an outing might do them both good…but it wouldn't really distract Sherlock, and would probably be a little too reminiscent of the past two months. What they really needed, what they were both waiting for, was confirmation that Moriarty's network was dissolved.

So he dropped into the armchair closest to the fire and resigned himself to making his request of the last person in the world who would probably fulfill it.

"I need a pick-me-up, of some sort, along the lines of an anti-dementor brew. You already know I'm bloody awful at Potions, this isn't anything I can manage. No, it's not for me," he repeated hastily, to forestall another jibe about unemployment.

"Who, then?"

"My flatmate. Sherlock."

Severus raised an eyebrow, and John fought back a mad urge to laugh again. As though anyone who had spent seven years in school with Remus Lupin could have failed to notice that every one of his half-dozen or so romantic interests had been decidedly female.

"And what is the root of this urgent need?"

Was he seriously…John couldn't believe his ears. As though Severus Snape weren't the last person—

Snape's lip curled.

"I'm not interested, Lupin. It's relevant to ingredient selection, not that I expect you to understand. What are you attempting to combat?"

"Apathy," said John flatly. "Depression. Worse than his usual lows."

"Surely Muggles—"

"—there's medication, yes, but it's less reliable. And he won't consider it. Might not consider this either, but I don't know what else to do. He's a chemist, so potions fascinate him. Might get him to take it in the name of experimentation."

Snape mulled this over, briefly.

"Causes?"

John thought. "Biological factors, mostly. Possibly social. Aloof is an understatement—by most people's standards he's the most unpleasant man I've ever met."

He caught Snape's pointed stare and didn't attempt to hide a grin. It faded, however, as he continued.

"And…elements of post-traumatic stress, I think. Sherlock is a detective by profession, but he spent the last year in hiding doing… a lot he was unaccustomed to."

"Just so we're clear, is this the flatmate who perished tragically a year before you dropped off the map yourself?"

It was John's turn to raise his eyebrows. Severus elaborated.

"The headmaster was, for reasons unclear to me…concerned."

Was he? John felt a touch of guilt. Yes, perhaps 'dropping off the map' directly following his forced resignation had been a rather…Sherlockian thing to do. Still, the mission had been secret. Dumbledore of all people would understand that.

He spoke shortly, making it clear he wasn't going into detail. "It was a government mission, over and done with now. There was violence involved, lots of it. I'm a soldier. He's not."

Severus turned his head slightly and John answered the unspoken question. "He was undercover. Hence the faked death."

"Undercover?" This time there was actually a hint of interest, albeit well-edged with mockery. Something in the tone made John's jaw tighten, though he met Snape's eye evenly.

"Not every Dark Lord is a wizard."

There was a long silence before Severus broke eye contact for the first time, his expression nearly indecipherable. John puzzled over it for a few moments before realizing it was recognition.

Recognition of…what had he said? Dark Lord, undercov—

Oh.

...oh.

And suddenly John found himself wondering how he had come to be sitting across from the insufferable git he despised, discussing the insufferable git who was his best friend, and whether they didn't have altogether too much in common.

He broke the silence.

"If you can help, I'd be obliged. If not, please relay the message to Dumbledore."

Severus nodded silently, black eyes now fixed above the mantle in a silence thoughtful enough not to be outright antagonistic. John supposed this was the best he could hope for, at least until Dumbledore made it back to Hogwarts. The headmaster would fulfill his request, John felt sure, though whether personally or by delegating it to a member of his staff remained to be seen… either way he'd at least relayed the relevant details.

The glow illuminating the elliptical office flickered abruptly into emerald as John flung his last handful of Floo powder onto the flames. When he glanced back over his shoulder Severus was still sitting in ponderous silence. The light playing over his sallow skin made him look like some unfriendly creature venturing up from the depths of the lake.

"Where have you been?"

John blinked. "You're up."

In a manner of speaking, anyway. The attempt looked to be more nominal than anything; Sherlock was lounged in his armchair, a duvet still wrapped around his shoulders. The microscope had taken up its old position on the kitchen table, surrounded by a number of moldy beakers and a couple of empty slides, as though Sherlock had been intending to compare the spores and lost interest halfway through.

Sherlock ignored the remark—or the back of his head did, anyway. John stepped out of the fireplace, not caring this time if he tracked ash onto a rug that had certainly seen worse, and circled the cluster of furniture to his own armchair.

"Where have you been?" Sherlock repeated.

John opened his mouth to reply, and stopped. "Deduce it."

Sherlock's eyes narrowed, and for a moment John wondered whether he would simply lapse into disinterested silence again.

"Somewhere within your own world, obviously, or you wouldn't have traveled by fire. You didn't bother with wizard attire, however—you're terrible at transfiguring clothes, but yours look the same as ever. Therefore, it was a private meeting with someone you're comfortable with."

John had to fight to keep a straight face at that. Not exactly.

"Possibly your cousin, Harry; you'd have worn normal clothes to avoid offending her, but there is no indication, olfactory or otherwise, that you've been near a tavern—"

Ouch. John winced, but Sherlock seemed not to notice.

"—no underlying scent of cigar smoke, although it's possible that the fire could be blocking that. Eliminating Harry, then, there's the other newly resurrected friend you've been so reticent about…Sirius, was it? However, if he's still on the run it's unlikely he'd be within a Wizarding dwelling, particularly not one connected to an active Floo Network. That leaves the headmaster of this school of yours."

John felt his mouth drop open, and briefly wondered how he still managed to be surprised, after all these years. He'd asked the question idly, partly for the sake of giving Sherlock's brain something to chew on and partly to reinforce the point that any serious involvement Sherlock intended in the magical world would involve wizards whose dealings would be much harder to trace than he was accustomed to. Who could, after all, disappear into thin air…

So much for that.

"Yes, okay," John admitted, though secretly it was a relief to see the old smirk fixed on Sherlock's face. "I visited Hogwarts."

"What were you doing there?"

"I'm not going to tell you."

"Why?"

"Are you going to tell me why this is our first conversation in three days?"

"You're not my mother," Sherlock snapped. This time it was John fighting to keep a triumphant smirk from his face.

Sherlock scowled, rearranging himself into an impossibly compact position and muttering something about 'insufferable, pointy-hatted ponces'. After a moment he ventured another question.

"Why didn't you Apparate?"

"Can't Apparate into Hogwarts," said John absently, flipping through the latest Daily Prophet, to which Sherlock had insisted on subscribing.

Sherlock sat up, suddenly intent. "Really? Why not?"

John glanced up. "There are wards."

"How are they set up?"

"Erm…" Somewhat startled at this abrupt line of questioning, John thought back to the once or twice he'd helped to ward a dwelling. "That depends on the type of ward. Almost every wizard lodging has some sort of basic defenses against other wizards, and Dark creatures specifically. I think the fancier ones require runes of some sort, but a basic anti-Apparition spell can be done with an incantation repeated at specific points around the perimeter—why do you ask?"

"It explains Mycroft's meddling, that's all." Sherlock glanced sharply at John as he did a double take. "His PA is a witch, didn't you know?"

Mycroft's personal assistant? 'Anthea', John supposed he meant, which…actually, that made her obsession with her Blackberry all the more confusing. But it wasn't really a surprise, all things considered…oh Merlin.

He groaned, letting his head drop forward and bump the edge of the coffee table lightly.

"He knows. He knew all along. He knows I Obliviated him…"

A smile stole over Sherlock's face. "Did you? That would explain why he didn't seem too pleased with you earlier."

"Mycroft came by?"

"Yes. And warded the flat. We're 'safe' now, apparently."

Well, that explained the microscope charade, anyway. John glanced through the kitchen doorway, his thoughts drifting. His trepidation regarding Mycroft aside, it was good to know that the flat had been warded, probably more competently than John would have been able to manage himself. Still, he'd made the mistake of trying to Apparate into a barrier before, and ached for days. It would have been nice to be given proper warning. Though given his last meeting with Mycroft…

Yes, that had quite definitely been a purposeful omission.

John kept his voice light. "What's the news on the network?"

Sherlock, still curled in his armchair, had been drifting into thought. Now his gaze slid toward John. "Nothing yet."

"Yet?"

"He said to give it another week."

John swallowed. "You okay with that?"

Sherlock frowned, the fingers of one hand tapping listlessly against the carpet. "Of course I am, I have to be, why wouldn't I be?"

John stood up, not sure what to make of this new, distracted Sherlock. It was an improvement over the past two days, he supposed.

"Care to help with dinner?"

Sherlock closed his eyes, and John sighed. "Thought not."

Sherlock's voice followed him into the kitchen.

"Are you going to tell me what you were doing at Hogwarts?"

John smiled in spite of himself. "Not a chance."

"John," Sherlock called.

It was two days later. Two days in which the detective had subsided back into his accustomed, sullen silence. Which was the reason the raised voice now came as something of a shock.

When John stumbled downstairs, hair ruffled from an afternoon nap and a hastily selected jumper, Sherlock was reclined on the sofa. Half-tangled in an old blanket, he had assumed what John referred to as his mind palace pose, fingers steepled over his chest.

"John, I unraveled your mysterious little Hogwarts excursion."

John was opening his mouth to ask what he was going on about when he noticed, out of the corner of his eye, a green glow dying from the direction of the fireplace. In the same moment another tall figure stepped into view. It took John rather longer than courtesy dictated to stop gaping and nod a greeting.

"Severus."

His knees weakened alarmingly as an insane desire to laugh took hold. Probably yet another sign that he hadn't thought this through; that the sight of Severus Snape's sneer bestowed on the (admittedly chaotic) interior of 221B left John with a sensation that two months' magical warfare against the late Moriarty hadn't managed.

The feeling that the walls were collapsing around his ears as his two worlds ran together.

It took another moment to realize that Severus was holding a sizeable bottle of a thick, highly unappetizing solution. The potion—Merlin, he'd actually made it. And hand-delivered it, no less…out of the goodness of his heart? More likely a threat from Dumbledore, or else…no. He couldn't actually be that curious, could he?

Either way, it was more than John had expected.

"Severus, I—thank you," he croaked out. Sherlock finally pushed himself upright, glancing from one to the other before focusing his attention on the tall, black-robed figure.

John tried again. "Sherlock, this is Severus Snape. Severus, my flatmate, Sherlock Holmes."

"Wizard, obviously," Sherlock half-muttered to himself. "Probability points to some level of professorship at that school—"

Severus raised an eyebrow. "Your perceptivity astounds me."

But Sherlock was just getting started. It was a token of John's state of shock that he actually had to turn aside to hide his grin as his flatmate steamrolled on.

"—indigo stain on the base of the left hand, but not from ink. That, and the slight condensation where your fingertips meet the bottle owing to the still-hot contents point to the conclusion that you made it yourself and delivered it immediately. Potions professor, then. When you entered, your gaze lingered on John's phone and laptop computer—" Sherlock spared it a glance, where it lay open on a side table, "—but not on the electric lights or kitchen appliances, indicating that only the more modern objects are unfamiliar to you. There are very few places in today's non-magical Britain where such devices aren't in use; inference: you grew up in a Muggle or half-Muggle home, but have since avoided the non-magical world completely. Whether this neglect stems from disinterest, unpleasant childhood memories, or the prejudice John mentioned remains to be seen, although the former can likely be ruled out based on an analysis of your wand."

John steeled himself and shot a sideways glance at Snape, whose usual impassivity had been overtaken with a calculating expression. If anyone else had been wearing it, John would have called it intrigue. Under the circumstances, it was ambivalent enough to be terrifying. Feeling that he'd be justifiably held responsible for Sherlock's admission into St. Mungo's if he didn't at least make an effort to shut down the running commentary…

"Sherlock," John tried, but Severus interrupted.

"My wand?"

"The handle, barely visible inside the pocket of your robe—hawthorn, is it? Difficult to tell from this distance—is well worn. At least two decades old, most likely your first and only wand. Sees almost constant use—much more than John's old one, which was more or less disused for twelve years, or his current one, which he only bought a year ago. His is polished occasionally, yours not at all. Therefore, you are not a man concerned with appearances, although the fact that you have retained the same magical instrument in working order so long indicates that you are a careful one. In short, a competent wizard, and unlikely to disregard knowledge regardless of its source. Additionally, one who keeps to himself, given the degree—" Sherlock stopped short, suddenly. "Why are you here?"

There was a pause.

"Why don't you tell me?" Severus suggested, assuming his usual dangerously silky tone as he straightened, the expression in his black eyes unreadable.

Sherlock waved this away. "You've obviously come to deliver that potion. You're not here to chat; it's clear from your demeanor that you despise John. The marked absence of his usual social proprieties shows that he's aware of the fact and uncertain how to respond. Still, he didn't neglect to offer a 'thank you' despite the fact that you've shown up unannounced—so, if you hate John, why are you doing him a favor?"

"Sherlock, I think that's enough demonstration of your deductive prowess," said John hurriedly, skirting a stack of books, but Snape waved a lazy hand.

"It's a bit late to start apologizing for your friends' lack of tact, Lupin. And, as it happens, I don't care." He turned to Sherlock. "Morbid curiosity and my employer compelled me here, if you would like to know."

"Curiosity?"

Snape's eyes slid to meet John's for a split second, and realization dawned. Of course. John had nearly forgotten the boggart Black, and the Sherlock who had appeared to make a fool out of him, but clearly Severus hadn't. That, added to the whole 'faked death' thing-well. Whether or not Dumbledore was involved, it wasn't at all inconceivable that curiosity could have driven Snape hither.

John hesitated, hoping to avoid that scenario being brought up, if at all possible. His usual diversion, however, which was to make a cup of tea, was useless in this situation. Whatever the measure of gratitude newly mixed into John's bitterness toward Snape, it was a singularly bad idea to prolong the awkwardness of this conversation. The very idea of inviting him to sit down bordered on ludicrous.

Snape seemed to sense, with no degree of heartbreak, that his welcome was spent; he clunked the bottle on the table in front of Sherlock without further ado.

"In any case, I'm not here for Lupin. This is for you."

Sherlock's eyebrows shot upward as he disentangled himself from his duvet, leaning forward to study the contents: thick and deep blue through the heavy glass.

"A potion for me…?"

And then the telltale furrow appeared in his brow, and the icy grey eyes flickered up to fix, not on Snape, but on John.

"So this was your errand?"

There was something dangerous in the tone.

"Sherlock," John started, for what felt like the fifth time in as many minutes, but Sherlock cut him off.

"I think I've made it clear before now that I have no use for your opinions regarding my mental health."

John's heart sank. Had he been that obvious?

"For Merlin's sake, Sherlock, it's just a pick-me-up!" he defended, swallowing thickly as he chanced another glance at Snape, and thanking whatever entities controlled the universe that he'd been frank about this possibility from the first. Severus, thankfully, appeared as unconcerned as though he were viewing a mildly interesting television program.

Sherlock scowled, but curiosity got the better of him long enough to pick up the bottle, turning it once in his hands. Then he held it up to the light, studying the viscosity.

"What's in it?"

"You don't want to know," said Snape bluntly. Sherlock cast a quicksilver glance upward.

"Try me."

"Antimony, lionfish, tentacula root, eye of newt, pomegranate juice, silverweed, and powdered dragon claw," Snape recited, looking bored.

"Antimony trisulfide? Is this an assassination attempt?"

For the first time, Severus smiled. The effect was rather like that of an escaped panther. "If that were the case, the potion would be for Lupin."

Sherlock snorted. "We all know you had your chance at that already."

Severus' eyes darted to John. "Did I?"

"John wouldn't have agreed to live anywhere near a school full of children unless his lycanthropy was under control," Sherlock pointed out, in the tone he generally reserved for the blindingly obvious. Snape's lip curled at that, though thankfully he kept silent. Sherlock continued, "Even if I wasn't already aware of his hopelessness in potion-brewing, the fact that John went to you for help is a dead giveaway. And despite your apparent enmity he trusts you not to poison either of us. Which, by the way, is a good deal more faith than he's ever shown me—"

"A good deal more than you've ever earned," John couldn't refrain from adding, glaring.

"—and given your position as Potions Master it's logical to assume that you regularly prepared the Wolfsbane Potion while John was at Hogwarts."

"Under duress, I assure you," said Snape smoothly.

"Go on, then."

"What?"

"Explain this," Sherlock said, tapping the bottle. "Antimony, you say? How is the toxin neutralized? Most of those other ingredients are relatively commonplace, so I assume the dragon's claw is the magically reactive component. Or is it something in the procedure?"

"That explanation requires an understanding of the effects of magical energy at the—"

"—molecular level," Sherlock cut in. "Yes, that's what I'm asking. For example, insofar as I've been able to determine, energy in the magical form springs only from sources within living creatures. Is that why the potion includes only biologically derived ingredients?"

There was a pause as the potions master stared at Sherlock, apparently weighing something…and John watched in astonishment and slight alarm as Severus sank, uninvited, into the black leather armchair.

"Yes and no," he said at last. "There is a category of abiotic ingredients used in potion-making, such as moonstone, but those are prepared beforehand and mainly serve the purpose of stabilizers. Chemically pure compounds such as Muggles use are neglected on the obvious grounds that such basically configured elements are held together by everyday forces, and therefore tend to be magically inert. The exceptions are…"

Torn, for the second time that evening, between hysterical laughter and sobs, John gave in to the inevitable and went to put the kettle on.

This was going to be a long night.

At seven o'clock, Snape was explaining the effects of clockwise vs. counterclockwise stirs, and why sets of seven revolutions were prevalent in the widely accepted Ptolemaic methodology.

At seven fifteen, Sherlock was postulating that the energy fields thus generated had a transformational effect on electron subshells containing the f-orbital.

At seven thirty, John realized he was hungry.

At eight o'clock, John realized he was starving.

At one minute past, he opened the fridge and groaned.

At 8:03, he pulled on his jacket and stumped to the door.

Sherlock and Severus were still wrapped in a discussion regarding the effects of nonmagically derived ingredients, reverse-orbital quantum physics, and the implications of magically directed forces in traditional forensic chemistry when John announced to the room at large that he was going to Tesco's. To his surprise, Sherlock actually paused in a detailed explanation of standing waveforms to acknowledge his departure.

In the form of derisive inquiry, at least.

"If food's so important to you all the time, John, why don't you try conjuring it?"

"Because food is one of five exceptions to Gamp's Law of Elemental Transfiguration," said Snape.

"Gamp's what?" asked Sherlock interestedly, turning back around.

John couldn't quite hold back a grin as the door swung shut behind him.

Sherlock was, in all honesty, fascinated. More than that. His mind was on fire for the first time he could remember in…eleven months? Twelve? How long since his usual intrigues had degenerated into an endless routine of hunt, slaughter, repeat?

This was magic with its potential gloriously unfolded. These were questions he'd spent the past year pondering over, with no time to indulge in research. Questions that John hadn't been able to answer, not even after a year spent as a professor—

I taught defensive magic, Sherlock, not magical theory. That's the sort of thing only brilliant nutters like Dumbledore are interested in…

Well, Sherlock Holmes was certainly brilliant, and John obviously thought he was a nutter, so he could hardly be blamed for considering this evening as very not-boring indeed.

Which John ought to be pleased with, Sherlock thought, throwing half a scowl at the potion bottle as Snape's explanation of basic transfiguration principles wound down. The thick glass seemed to wink at him, dully, and something occurred to Sherlock, not for the first time.

"Does one have to be a wizard to brew potions?"

Snape considered. "There is some degree of controversy. It is, in my opinion, feasible; provided the environment itself contains a sufficient concentration of magical energy. Hardly a resource that most Muggles have access to."

Sherlock's shoulders twitched impatiently. "And would John's presence here provide that?"

Snape's lip curled slightly. "Possibly. The presence of Dark magic in this flat—"

Sherlock interrupted, sharply. "Dark?"

"Yes." Severus straightened. "Your 'flatmate' is a werewolf, there's an inherent Darkness in that bite. Everpresent, even if it only surfaces once every lunar cycle. His own feelings on the matter are irrelevant."

"Wherein lies the distinction between Dark and Light magic?"

"Where wizards are concerned…intention. With other creatures, it's a matter of nature."

Sherlock's grey eyes swept him. "You've made a study of this."

"The dual wizard/werewolf presence in this flat will most likely provide the level of magical energy necessary, though there are certain spells he could cast to reinforce the effect. More than that I can't say. You won't find it difficult to acquire the basic potions kit and get started, though Wolfsbane might be out of your reach just at present."

At present, perhaps. The discussion of John's lycanthropy led into another thought.

"Why does your presence make John feel guilty?"

Snape narrowed his eyes, taken aback. "Why do you say that?"

"Please," Sherlock scoffed. "It's written all over him. Just as abject loathing of the world at large is written all over you."

Snape's nostrils thinned.

"I can only assume that Lupin has the decency to regret old wrongs, even if he lacked the spine to put a stop to them."

Sherlock drew back slightly. "What do you mean?"

"Merely that the world in general takes a narrow-minded view of whatever it labels an oddity, and your friend is no different."

"No different?" Sherlock scoffed. "I think I'm proof against that assertion. Besides, John was bitten by a werewolf at age seven. Surely that's a substantial step toward any definition of oddity."

"The best that could be said in his youth was that Lupin was careless, indiscrete, and slightly less insufferable than those he called friends. One of whom, in case you haven't heard, betrayed the others and killed a dozen people before spending a decade in Azkaban."

Sherlock turned this over in his mind. The information about Sirius was old, not to mention faulty; it didn't concern him. The description of John was more intriguing, in that it explained Snape's obvious animosity. Although it did present a ludicrous contrast with the John that Sherlock knew. After all, he'd been called freak and a thousand other less savory labels all his life, and John was the only one who absolutely hadn't cared…

He didn't realize he'd voiced this last bit aloud until Snape's sneering tone interrupted.

"Possibly you're his attempt at atonement."

Atonement. There was that word again. In an entirely different—or, no, perhaps exactly the same—context than John had used it. Not that Sherlock considered any schoolmate jaded enough to retain his bitterness for nearly two decades an impartial voice on the matter. Nor did he particularly care about John's past transgressions, except insofar as they related to his as-yet unexplored web of associations within the magical world. Which meant, Sherlock supposed, that John's emotions did matter on some level. Though he'd seemed more bewildered than bothered by the afternoon's turn of events.

An unfocused part of his mind snagged and replayed the last few seconds again. Snape's expression had shifted, suddenly, a reaction to…what was it? Ah, the word freak meant something to him too, apparently…not Sherlock's affair, however. Not when there were much more interesting matters into which to pry.

Bait the trap. Carefully.

"So." He gestured at the blue bottle. "How does this work? Stimulation of dopamine transmitters?"

He met Severus' carefully disinterested gaze, smiling inwardly. It was astonishing how people let their guard down when one revealed a crack in the armor. However counterfeit-or at least, artfully revealed. Yet another reason to have armor in the first place.

Unlikely that anyone he'd just met, (let alone a man even more standoffish than himself) would actually care on any genuine level, but that didn't matter. If anything, it would help: Snape didn't know him well enough to detect anything suspicious in an uncharacteristic degree of candor. And if Sherlock's suspicions regarding the parallels in their situations were correct, mere curiosity would string him on.

Curiosity. The word sparked something in his mind. Another outlet to explore…

He was distracted by Snape's reply.

"I believe so."

"And John thinks this is a necessity because…" Sherlock let the gesture and the word trail off.

"Something about personal demons and the tragedy of childhood neglect finally catching up with you."

Sherlock raised an eyebrow; like most of John's theories, that was both mildly perceptive and completely wrong.

"Really?"

"No. He mentioned trauma related to your undercover work."

Oh, that was bloody perfect. As though after two years John didn't know…

But however annoying the revelation, it did allow one piece of the puzzle to slot into place beside the other bits and pieces he'd gleaned from John. More firmly, anyway. Despite their mutual dislike, John trusted Severus Snape.

Why?

Was he simply entirely blind to what Sherlock could see? Did he have more data, a better, more definite interpretation?

Or did he simply trust him because Dumbledore did? And if so, would he trust him without the headmaster to keep him in line?

All irrelevant questions. Until such time as Lord Voldemort saw fit to rise again, and the blindingly imminent wizard war was upon them. It never occurred to Sherlock to simply stay out of it. (In fairness, it certainly wouldn't occur to Mycroft either.)

"Interesting theory," Sherlock drawled. "Did you offer any of your own insight?"

Severus inclined his head slightly, one corner of his mouth twitching in the suggestion of a deliberately artificial smile. Body language relaxed, Sherlock noted, but not uncharacteristically so. All right then, he was very good. Although certainly that was to be expected. Given what John had said, Snape was probably used to direct intrusion into his thoughts.

But the question was too casual.

"Insight?"

"Regarding the taxing nature of undercover work," said Sherlock calmly.

Severus' eyes widened in a parody of sincerity, and Sherlock nearly laughed aloud. It hadn't taken him long to catch on. Which, of course, meant Sherlock would have to tread carefully from here. Timing.

"I can't imagine why you should think I would have any particular perspicacity in the matter."

Why, indeed. Sherlock sat back, regarding the Potions master over steepled fingers, unaware of the irresistible comparison springing to the other's mind.

"Can't you? It's obvious to me. I can only hope that Lord Voldemort can't—ah." Sherlock closed his eyes. "He does see. Or did, and will again. You're the emissary then, playing both sides, the central piece in a game of back and forth, depth and perception. Not so different from one I once played myself."

And am playing still. It was astonishing, amusing really, how simpleminded John could be at times. As though Sherlock could ever be persuaded into this hellish, weeks-long entrapment over the hazard presented by a few surplus thugs who had absolutely no motivation to risk their own freedom by threatening his life, or John's. As though dismantling the network hadn't merely been the next move in a game that ran deeper and deeper, one lie buried beneath another until they simply ran out of words to stand on. And then, there were hints. Gestures as insignificant as the tap of a finger or as grandiose as the fall off a building. The cue for round two.

Once, Sherlock had thought it might last forever. There was a bizarre sort of contentment in the idea. But then had come the looming threat of losing John, not once but twice, no, three times, indirectly, when he'd disappeared and not even Mycroft had been able to ferret him out.

And now another war loomed on the horizon. No, Moriarty's game was over. Soon. That didn't mean Sherlock couldn't get a head start on this one in the meantime.

Snape was regarding him from behind the impartial mask. "Where, may I ask, is the string of deductions this time?"

"I'd rather discuss things I don't know. For example, who wins?"

"I don't follow."

"The winner in this war is whoever takes home the prize of your allegiance," asserted Sherlock, drumming his fingers against his knee. "It's not an irrelevant question."

Ridiculous, of course it was irrelevant. Or rather, even if the question was pertinent, any answer would be a tautology. Immaterial. Sherlock wasn't looking for answers; he was browsing for reading material.

Snape offered one anyway, after a pointed scan of the room and the unarmed detective.

"You seem to have determined that already."

Sherlock scoffed. "In the event you are truly Voldemort's lap pet, any harm done to me would be showing your hand far too soon. And in any case," he raised his phone, displaying the time, "John should return in roughly fifteen sec—"

There was a ring and Mrs. Hudson's muffled fluttering downstairs, and then John's footsteps ascending the short flight. He shouldered his way into the room, bearing a stack of takeout boxes in one hand and an armload of groceries in the other.

"Hello again," he said, still wearing that faint, bemused look. "Did you manage to deconstruct Agrippa's Semi-Intransigent Theory of Dualistic Electron Deportment while I was out?"

Severus raised an eyebrow and let that question fall to Sherlock, who merely smiled.

"I rather think we did."

Severus left, shortly after John came back. John was rather grateful, as he wasn't sure his paradigm could have handled an evening of Thai takeout and telly with the world's only consulting potions master.

The next day a battered old textbook appeared in the fireplace. Beside it lay a long, tawny feather, shed by an impersonal barn owl of the sort that Wizarding schools and post offices recruit in large numbers. Advanced Potion Making by Libatius Borage, proclaimed the cover.

Sherlock continued his lethargic vigil on the sofa, flipping through it.

Severus despised owls.

The blue bottle, its contents now cooled, assumed a position of honor beside the skull on the mantle. Sherlock never touched it, as far as John knew.

John retained a thoughtful silence.

Sherlock made John recount the tale of the boggart that had generated such morbid curiosity in a man even more famously misanthropic than himself. Later he pestered John into arranging a reunion with Sirius Black—if only to achieve it in person.

The upper floor of 221 Baker Street filled with potion fumes and the days with a hitherto unprecedented quantity of minor explosions. The dwindling of John's Gringotts account became a thing of the past, though Mrs. Hudson did occasionally add damages to the rent.

Severus Snape chose a side.

A Dark Lord rose again. The inhabitants of 221B fought back in their own ways. And quite enjoyed themselves, though only one of them would admit it.

. . .

But most of that happened later.

. . .

That night…well, that night John wrote in his blog.

Due to the International Statute of Secrecy, I'll never be able to post this one. But believe me, it's well worth chronicling…