A/N: Someone requested a sequel with Sherlock helping Snape. I hope this meets expectations!

The forest was foggy in a way that consumed light rather than reflecting it, that pressed utter darkness upon his senses. It was so different from the half-hearted suffusion he was accustomed to in London, and that, in some ways, was a relief: to feel himself invisible without the familiar necessity of dodging behind phone boxes and into alleyways. In others, it felt like a trap. As though the snap of every twig and hoot of every owl was ready to proclaim him for what he really was, to splash his conniving across the forest floor for his adversary to see and for himself to slip and break his own neck.

In Sherlock's experience, a good hunter always felt like the hunted.

It was right, it was necessary. It kept him on his toes, anyway, which might save his life in this encounter, underpowered as he felt without so much as a handgun at his side. Hopefully the deception would come off nicely, Sherlock thought, stroking the unfamiliar narrowness of his nose, and things wouldn't come to blows at all. There was no reason that they should. Still, he couldn't but curse for the thousandth time the wasting hex that had sapped away at his magical energy for years now, a little more every day. It was doubtful at this point whether he would be able to perform so much as a Stupify if the need arose; even his well-polished wand was beginning to feel alien in his hand. Soon he'd be no better than a Muggle.

A blazingly intelligent Muggle, of course, but a Muggle all the same. Intellect is of limited value in a firefight, of infinite value in avoiding them. Sherlock had taught himself with grinding regret to bow to the necessity of the latter.

Yaxley had arranged to meet him in the hollow. That was typical enough. Until Lord Voldemort chose to come out into the open, his followers were stuck in meeting places like this: rugged patches of countryside, to which few of the magical bourgeois that formed the core of the Death Eaters were accustomed. They held their tongues, in the presence of their lord at least.

For his part, Sherlock didn't mind the woods. They brought back comforting memories of his own solitary childhood rambles in the country. The Holmes parents, for reasons best known to themselves but easily guessed at, had given up early on integrating their children with those their own age, which left Sherlock and Mycroft free to do as they pleased. For Mycroft, that meant air-conditioning and endless textbooks. For Sherlock, it meant the freedom of the outdoors. But for Yaxley's sake he plastered an expression of displeasure across his face as he came into the wavering circle of wandlight in the clearing.

Severus came by Floo again, for obvious reasons. No sense attracting attention to this 221B Baker Street if he could help it. It was unlikely that Voldemort was still having him tailed - not after their nice little chat last summer had hashed things out between himself and the Dark Lord, and reassured the latter of Severus' loyalty - but still, it made a good deal more sense to step into Dumbledore's fireplace than to leave the castle grounds and Apparate onto Holmes' doorstep.

Holmes' doorstep. Lupin was an afterthought by now. Also absent, if an initial glance about the flat was anything to go by. The room wasn't empty, however. A tall figure clad in the Muggle equivalent of dress robes stood beside the opposite wall, back to Severus, facing a mess of string and unmoving newsprint that had been tacked over the hideous wallpaper. Severus took a moment to regard the figure, which he remembered as rather a pathetic collection of thin limbs and blue dressing gown bundled into an armchair.

Without turning, Sherlock waved a hand in his general direction.

"Sit down, Severus, I'll be with you in a moment. Mind the carpet. The landlady's rather particular about that sort of thing."

Severus glanced briefly downward at the ash on his shoes, then raised an eyebrow as he surveyed the flat again. The 'particular landlady' in question appeared not to have made her presence known for some time. The flat was, if possible, in an even greater state of disarray than it had been during his one previous visit. Scraps of paper cluttered the floors as well as the walls. A mound of unused yarn sat atop a pile of dog-eared books on the mantle. A glass case of beetles lying on the coffee table had been wrenched open, with two specimens missing; by the familiar bubbling of a cauldron in the kitchen Severus thought he could deduce where they had gone. The dining table, groaning beneath mounds of dishes and Muggle chemistry equipment, appeared not to have been touched in the past year and a half.

"Lupin's out?" he inquired, brushing a werewolf hair or two from the Union Jack cushion before lowering himself gingerly onto the sofa.

"Locum work," hummed Sherlock vaguely, pressing a tack into the wall. Moments later he gave a whirl worthy of Albus Dumbledore and settled into his leather armchair, regarding Severus over steepled fingers. The latter barely refrained from rolling his eyes. Whatever brand of eccentricity was meant to accompany genius, Severus hadn't got.

"You knew it was me," he said, to break the silence. "Not many magical visitors, then."

"Not many who enter as quietly as you do without announcing themselves."

Severus nodded. Lupin was deeply involved in the Order, that he knew. It shouldn't surprise him that Albus had thrown in the towel on the Statute of Secrecy where his perspicacious flatmate was concerned.

"John's in it neck-deep," said Sherlock, reading his mind, "now that the loose ends of the Moriarty case have been tied up. But you already know that."

"And you?"

Sherlock made a sound as eloquent as it was rude. "His mild-mannered Muggle roommate? What do I have to do with anything?"

His obvious bitterness made Severus tighten his jaw in satisfaction.

"The blindness of my colleagues comes as no surprise to you?"

"Hardly. Muggles are much the same."

"Then, to what I am sure will be the intense displeasure of our combined pool of acquaintances, I'm here to offer you a job."

Sherlock blinked to hide his surprise. "Severus Snape, my client?"

"If you insist."

The detective tapped a finger against the chair. "It could be argued that I owe you."

"That won't work on Lupin. Not once he hears what I have to ask."

"Need he hear it?"

Severus gave a very slow, very rare smile, the effect of which had once been to make a first-year break out in sobs in the middle of class.

"I see you and I are once again of the same mind."

"You're after some good, old-fashioned espionage, I'm assuming."

"Naturally. The majority of my colleagues couldn't fashion a lie to fool a particularly dim-witted mountain troll."

"Clearly not, if you're more concerned about their playacting than my lack of magic. Whom will I be impersonating?"

"A minor Death Eater. A man named Florens. He's been given a task by the Dark Lord. I want you to fulfill it."

Sherlock raised an eyebrow.

"Dispatched or imprisoned?"

"The former."

"By you?"

"I didn't know about the special assignment at the time. There is nothing easier than disposing of a corpse by magic, but if he fails to complete this task…"

"Then Voldemort could conclude not only that Florens dead, but that he was killed because of the task itself. Which would give him cause to wonder if there is a mole in the ranks."

"A blunder," Severus said, running his tongue across his lower lip. "I call it what it is. But the incident was life or death. Florens was stalking a Muggleborn witch, and the lack of witnesses decided me in favor of a rare intervention. People vanish in wartime. It wouldn't ordinarily be brought to the Dark Lord's attention."

"Bad luck."

"And probably a waste of time, a drop in the ocean. Voldemort is escalating to an open season on Dumbledore supporters, and as you can imagine, that complicates my role considerably."

Sherlock nodded. "Save an innocent, risk your position in Voldemort's court."

"Some interventions can be explained away by the necessity of appearing loyal to Dumbledore. This one can't, for the very reason that there were no witnesses."

"And you, naturally, can't impersonate Florens yourself."

"We must be seen, if not in the same room, at least at the same time."

"You're not sending me to Voldemort's side?"

"You're incapable of Occlumency - shielding your mind from intrusions. It's too great a risk."

Sherlock bit back his disappointment, making a mental note to inquire of John about mind-reading. "To whom, then?"

"A partner in crime. Yaxley. The two of them have been instructed to destroy London Bridge in such a way that Muggles and wizards alike believe it was caused by a Muggle attack. Or, at least, that it could have been. The Dark Lord is not ready to emerge into the open, not yet, but he is not averse to priming the stage. Creating an atmosphere of terror."

"And are we to effect this attack using Muggle methods?"

Severus snorted. "Yaxley is neither that resourceful nor that intelligent. Your job, obviously, will be damage control. Bonus points if you manage to tip off the Ministry in a way that doesn't look like betrayal of the Dark Lord's cause."

"If you tip them off yourself…"

"Then the Dark Lord will know there is a traitor in his ranks. No, whatever process you put into action must be transparent to Voldemort. Yaxley must survive to report on the ordeal…though whether he will survive the Dark Lord's wrath is yet to be seen."

Sherlock nodded again, absently. "So my participation…"

"Will consist in a single meeting."

"With Yaxley alone?"

"Yes."

"How well do the two know each other?"

"Moderately."

"You have background on this Florens?"

Snape handed him a file.

"Department of Magical Accidents and Catastrophes," Sherlock read. "He's a Calamity Investigator? Calamities of what sort?"

"Any suspected to have been caused by magical means or creatures."

"An intelligent choice for this mission."

"And a loophole for you to exploit. Continue the misdirections that Florens has no doubt already been feeding to the Ministry…"

"...but do it worse," Sherlock finished. "And, if possible, with Yaxley's approbation. When the Ministry cottons on, Voldemort will blame the senior Death Eater."

"Florens, naturally, won't make it."

Severus shrugged. "Occupational hazard."

"Speaking of which…"

"Yaxley is powerful, but not clever. You should have no problem soothing his suspicions. I've included photographs in that file for you to get an idea of his mannerisms. Your disguise will be simplicity itself. Have you brewed Polyjuice yet?"

"Obviously. I'm a detective."

"Not so obvious when you've spent fourteen years watching beginning potioneers mangle the simplest of Sleeping Draughts. You've made progress."

"I'm not an eleven-year-old," said Sherlock simply. "That gives me an edge. As does this, for which I never had occasion to thank you."

He pulled a well-annotated and dog-eared volume from the bookshelf behind him. Severus spared the old Potions textbook a glance.

"Keeps it out of the hands of my meddling students."

The corner of Sherlock's mouth twitched. He'd had John test out a few of the spells written in the margins…on inanimate objects, of course. The majority of them bordered on very obviously Dark Magic. It was a six-form book, and the youthful hand in which the annotations were scrawled could not have been beyond its teens.

"Nonetheless, we'll consider it more than adequate payment for this job. Unless of course I end up dead, in which case, work it out with John, won't you?"

"Don't end up dead, Holmes. The last thing I want is to spend my life brewing Wolfsbane for your orphaned pet."

"I would advise you to hold your tongue when John gets here, but that title would actually strike him as far less offensive than what the tabloids generally assume."

Severus' expression darkened. "I thought we were doing this without Lupin's involvement."

"I'm reevaluating that. Mind-reading is a possibility, you say?"

"Yes, though a slim one, where Yaxley is concerned. It requires more finesse than I know him to be capable of."

"But there's also the issue of magic. If he finds out what I am, he'll kill me outright."

"Obviously. I can give you a false wand pre-charged with one or two spells, and teach you how to use it, but that's all I can do."

"All you can do, perhaps, because you won't be on hand."

"If you're thinking of handing over this job to Lupin…"

"Of course not. John has many talents, but dissimulation is not among them. Truth be told, it's not my life I'm concerned about, Severus, but yours. Or, more precisely, the collapse of Albus Dumbledore's plans involving you."

Snape paused. "I can't deny you know a good deal than you should."

"Automatic deductions." Sherlock waved a hand. "Can't help it. No, much as I loathe the idea, I'm forced to wonder if this knowledge can be placed behind a…a mental block of sorts."

"Magic can be used to modify your memory."

Sherlock was silent.

"No," he said finally. "It won't come to that. But I will require John's help. Which means that you and I have a very long afternoon ahead of us."

Severus shifted impatiently. "I'm hardly going to be of any use in persuading him."

"No. But with you around, he might think twice before putting me in a Full-Body-Bind to prevent me from going on the mission."

Two hours after John got home, Severus finally deigned to speak to him. Two hours was how long it had taken Sherlock to convince his flatmate not to prevent him from going on the mission, and now the three of them sat in utter silence, Severus and John avoiding one another's gazes, and Sherlock a million miles away, fingers steepled beneath his chin. John was nursing a mug of tea in silent fury. He had very pointedly refrained from offering a cuppa to Snape.

"What's he doing?" asked Severus finally, as the daylight faded. "How does he propose to alter his memories without magic?"

"That's what he's testing, I reckon," said John, when the silence had stretched on just a little too long. "He uses a memory technique. Calls it his mind palace. Files away anything he needs, and deletes any information that he considers too mundane."

"He's deleting any compromising knowledge?"

"At least temporarily," said John, without looking at him.

Snape risked a glance at Sherlock, whose only movement was a silent muttering to himself. It was clear from the professor's sneering features that he was more than uncertain about these methods.

"Holmes is correct that the odds of his undergoing Legilimency are vanishingly small. But it would surely be more prudent to delete the compromising memories by charm."

"He'll never allow it, and nor will I."

Severus raised an eyebrow at the finality in Lupin's tone, but said nothing.

"You say he will be able to re-access these memories later?"

"He's explained it to me before," said John, "a bit. If this works it will be the ultimate in method-acting. He can think himself into a different person. The problem will be drawing him out again."

"Insane," said Severus flatly.

"Yes."

"Yet he's done it before."

"Not to this extent, I don't think."

Under their combined gaze Sherlock roused a bit, blinking at them both. "John?"

"Sherlock," said John, fighting to keep his expression blank. "Who's this?"

He waved a hand at Severus. Sherlock followed the motion, looking him up and down.

"Hogwarts professor. Potions. Probably a half-blood, going by the-"

"Polish of my wand, yes," interrupted Snape, as John gave his flatmate a nod. "This had better not be a charade concocted by the two of you."

"How could it?" snapped John. "I wasn't aware that you were planning to send my best friend into mortal danger until a mere two hours ago."

"I hate to tell you this, Lupin, but your best friend lives in mortal danger."

"Quit bickering." Sherlock was slowly coming back to life, looking from John to Severus and back again. "I don't quite recall what's going on, only that you," he pointed to Snape, "have given me a task, which for some reason I'm inclined to fulfill, and that it's fairly urgent. Where's that file…and where did I put my wand?"

John and Severus looked at one another.

Oh no, was all John could think. He's made himself a wizard.

Sherlock needn't have bothered to adopt any Death Eater mannerisms. The fool didn't so much as attempt to verify Sherlock's identity before leaping into their plans. The workings of the senior Death Eater's mind were, it seemed, approximately as blunt as his features.

"You take the south bank, I'll take the north," Yaxley grunted. "I don't see what else there is to discuss. We'll do it during - what do those swine call it? During rush hour, when the bridge is packed with those -"

"Automobiles," Sherlock supplied in a disinterested tone.

"Yes. A routine attack. What are you so concerned about that we have to discuss further?"

"Even the smallest of the Dark Lord's plans is worth extensive preparation," Sherlock asserted, drumming his fingers against his thigh as though in irritation. "But in this case, it's not a routine attack, it's an escalation. This isn't just about disrupting Muggle infrastructure and economy: in the minds of Dumbledore's followers, these Muggles are actual people, their deaths worthy of investigation. An attack on London Bridge will have even that fool Fudge wondering if the Dark Lord is behind it."

Yaxley grunted. "That's the idea, isn't it?"

"Get them wondering, yes. Reveal our hand entirely, no. Muggles have terrorists of their own, of course, but there are already suspicions in my department that some of the calamities we've been dealing with-"

"That's why the Dark Lord put you on this assignment."

"As far as allaying them goes, I've been pushed to my limits already. No, the Dark Lord wants me on hand to misdirect the routine London task force prior to the attack. It's doubtful whether I'll be able to get there in time to assist you."

"He said nothing of this to me."

"I'm afraid he may have considered it a little…obvious. But you're free to go to him with your concerns."

Yaxley's nostrils flared. "Remember your place, Florens."

"My place will likely be within the Department of Magical Accidents and Catastrophes itself. I can misdirect the Aurors long enough for you to finish the job. Or, we skip all that in favor of a blunt-force attack." Sherlock shrugged his thin shoulders. "It's your decision, Yaxley."

He had layered the conversation carefully. A foundation of logic that not even Yaxley could resist. The implication that Voldemort knew, and approved of, Florens' version of the plan. A dig at Yaxley's intellect, a reiteration of the logic, and finally, an unexpected appeal to Yaxley's sense of superiority as the senior Death Eater. A partner a good deal more intelligent would not have taken the bait (might have asked, for instance, whether Florens' interference within the department wouldn't cause just as much suspicion as the attack itself). Yaxley, however, took it.

"We'll do it your way, Florens. And the Dark Lord will know that, if this goes south."

And not otherwise, of course, Sherlock thought, hiding these private musings with a respectful nod. Prodding at an ego like Yaxley's was like playing with fire, and he had done quite enough of it for one night. It was time to report.

And Sherlock turned to leave, relieved at the earsplitting crack that told him the Death Eater had Apparated away first.

Sherlock cradled his head in his hands. It was a lot to take in.

"Let me get this straight," he said, to no one in particular. "I'm not a wizard?"

"No, and I'm not even going to ask how you convinced yourself of that in the first place," said John, rolling his eyes. "Did you actually try any spells?"

Sherlock looked at the false wand on the coffee table.

"None, though I recall now that I could have done. Severus said he modified this from the trick wands sold in wizard joke shops. Only takes a wave."

"We'll save the charges, then," said John, eyeing it warily from his place by the window. "Because, unfortunately, I think you're going to need them."

Sherlock cracked one eye open.

"Repeat employment, do you suppose?"

"Don't expect me to like it," said John wearily. "But, yes. Bridge destroyed by clearly magical means. Ministry tipped off. Florens with a proper excuse for being dead. Voldemort furious with Yaxley…"

"...and that idiot Minister of yours still refusing to believe a word of it," said Sherlock with some venom.

John shrugged. "Doesn't matter. The more Fudge blusters, the more of a mere figurehead he becomes. Intelligent witches and wizards within the Ministry are finally beginning to ask the right questions, put the right precautions into place. You've saved lives, Sherlock."

"So you're not going to attempt to stand in the way of future missions?"

"I think Mycroft is going to pose a greater obstacle than I ever could," said John, gesturing toward the window, where a black car was pulling up outside. "And truth be told, I'd like to join him. I've lost too many friends already to this bloody stupid war."

"Mycroft hasn't a leg to stand on. He sent me on a global one-man search-and-destroy mission, for heaven's sake."

John shook his head. "The magical world's different."

"Not that different."

"Oh?" argued John, as a set of heavy steps ascended the stairs. "You think it's just going to be a quick chat in the woods next time, do you?"

"No," said Sherlock simply. "I think that next time I'll probably have to do some magic."

"That false wand of yours isn't going to cut it."

"No," agreed Sherlock. "But you are. Wingardium Leviosa."

He snapped his fingers, and after a moment John cottoned on and levitated a half-eaten slice of toast from its place on the coffee table.

"We'll work on timing," yawned Sherlock.

And John, in spite of himself, could only smile.