Author's note: A gift for the lovely people on Tumblr who expressed a wish for a love potion fic :) The last chapter will move into smuttish territory, so if that's not you're cup of tea, you've been warned.

I will try to upload the next two parts within the next couple of days! (honestly, the fic got away from me a bit and turns out it will be a bit longer than a one-shot)

Also, a great big thanks to my beta Desert Child for being incredibly patient with me and my other story! This little fic served as a means of breaking my writer's block :)

Enjoy!

Chapter 1: Light, heat, pressure

Glasgow

The clanking of cutlery against fine china rang through the air. Minimalist lamps and elegant chandeliers spilt warm light over the space. Waiters swarmed about like a flock of blue jays, smart in their uniforms, with platters balanced at the tips of their fingers. The air outside smelt of rain, early breath of autumn, wet paving stones, and the unique smell that old cities had at night. There was nothing out of order about that particular night, or that particular restaurant, apart from the fact that in the men's restroom, next to the mirror, Henry Knight was kissing a man he really never thought he would be kissing. Kissing him against the wall, and against his better judgement.

On the other side of the country, Sherlock Holmes had just given up smoking again, unaware that the abstinence crisis that would hit in a few days would lead him to make a completely inane decision. And then change his life.

221B Baker Street, London, a few days later

A shave. That was what Henry Knight needed, if you asked Sherlock. And possibly a tutorial on how to use cologne properly. The current, honestly appalling amount was making it hard for Sherlock to sniff at the residues of cigarette smoke that still clung to his client's clothes. The itch under Sherlock's skin intensified. He wanted nicotine, and the patches weren't doing it.

Henry Knight kept on gazing around the flat, idle and slow. It was positively astounding that he could not hear Sherlock's teeth gritting. John would have definitely noticed, were he in the flat. Which he wasn't. John was taking a walk. John had been taking walks rather often lately. Determining the reason why was one of Sherlock's primary mental exercises. So far, the circumstances that prompted such walks were always too different to constitute a logical pattern. Which was interesting. The only thing more intriguing than a pattern was a complete lack of one. John's behaviour followed no pattern (the same could not be said about his jumpers, which all, sadly, followed the same one: tatty with a thread of 'really-John-what-were-you-thinking' running through them). John's behaviour was erratic, Sherlock concluded for the umpteenth time, his leg bouncing rapidly, heal hitting a muffled staccato on the carpet. Only, Sherlock was sure it was not, sure that there was a common denominator to all the times John had inexplicably decided to go for a stroll. Sherlock stood up, vaguely aware of Henry Knight blathering on about how he found out about Sherlock's services in the first place. The man stammered just slightly, fumbled over his words. Deeply rooted trauma, then. Or, possibly, an impactful event, rather recent. Probably one or the other. Typical.

Not like John. Irregular, confusing John. Mind-puzzle John. Sherlock turned his back to his client, and faced the mirror. There was something about John's walks that he was missing. A link or a catalyst he had yet to identify. Sherlock felt like the answer was staring him right in the face. Just slightly out of reach. And Sherlock's reach wasn't easy to escape, so really, this was impressive. Unlike the blabbering man seated in John's chair. Sherlock spun on his heal and rounded on his guest, interrupting him mid-sentence and forever depriving himself of the knowledge what precise technical issue prevented Henry Knight from finding out about Sherlock a full day and a half earlier. A true tragedy, that.

"Mr Knight, you said that this case of yours could not be properly presented any other way than in person. Seeing as you are here now, please, do try to convince me."

The other man regained his composure impressively quickly, considering that he had suddenly become the seemingly sole focus of Sherlock's attention, where the detective had appeared to be thoroughly ignoring him just the previous moment.

"Um, yes, well. As I just said, once I've managed to find your contact information, I knew you were the man I needed. You see, Mr Holmes, I needed you because I have been poisoned."

This semi-dramatic confession was met by a single arching eyebrow. When Henry stayed silent, Sherlock prompted. Well, so to say.

"For a poisoning victim you appear to be doing rather well. No signs of organ failure, sepsis, or death. I prognosticate a full recovery. Was that all there was?"

"Mr Holmes!"

Finally the man was showing some spirit. Sherlock sat back down, and motioned for Henry to continue. The other man swallowed and then spoke.

"I am not dead or dying because I the poison I have been given was not a...typical one." Another pause. Sherlock was wondering if he had time to produce some cyanide from apple seeds and put himself out of misery of this interview. At least Henry took out a cigarette and lit it after getting a nod from Sherlock, so Sherlock could finally indulge in a bit of passive smoking. He sincerely hoped the poison would turn out to be something exotic and useful in future experiments.

"What I have been given, Mr Holmes", finally Henry resumed,"...is a love potion."

Well then. Not really exotic or useful. But most of all, very, very inexistent. Sherlock's sigh could have knocked down brick houses.

"Mr Knight, if you came here to waste my time, then I –"

"I have not. I swear I have not. You have to believe me, Mr Holmes." There was a firm urgency to Henry's voice that convinced Sherlock the man was either serious or seriously out of his mind. Possibly both. Probably both. Still, Sherlock had nothing better to do at the moment. And listening to Henry would mean more smoking. Honestly, the smoking was a rather appealing idea. Sherlock knew how to make good of a bad situation, so he decided that Henry could stay as long as he kept smoking, and Sherlock would listen. Or at least pretend to.

"Alright, so what are you saying about this 'love potion'?"

Henry drew a puff of smoke before replying.

"I live in Dartmoor, bit outside the town, so I have all my groceries delivered. I order them online."

Sherlock couldn't contain himself. Really, he was doing spectacularly well, even without John there to shoot him warning looks. But then again, he was only human (not that he would ever admit it).

"Did the delivery man bring you a love potion instead of milk, then?"

Henry didn't seem deterred by Sherlock's mockery. Sherlock presumed that when one went around claiming to have been given a love potion, one had to develop some sort of immunity against mockery.

"No, he did not", answered Henry. "But he did bring a different brand of sugar than I usually took, not the one I ordered, you see. I didn't think anything of it then. I was going on a trip the next day, so I didn't have time to make a fuss about it."

The story started to take shape in Sherlock's mind, almost against his will.

"Naturally, you drank your afternoon tea – two sugars, no milk – and then again in the morning, coffee, before catching your train."

If Henry was a bit dazed by Sherlock's interruption, he recovered quickly and picked up the story where Sherlock had left it.

"Yes. I went to Glasgow, for a business trip and to visit an old...friend of mine. Nothing felt off until I got there. I was supposed to stay with him, you see. A two day stay. I arrived on Tuesday, planning to sleep over, head out for the business fair on Wednesday, and catch a train back home later on." Henry's cigarette kept burning itself to a stub while he spoke. "But that first night...I don't know how to describe it, Mr Holmes."

"Why don't you try anyway?" Sherlock's leg was bouncing again. Henry stubbed out the cigarette and reached instantly for a new one. His hands were shaking.

"Yes, right...We met up at a restaurant. I haven't seen Christopher for months. We've had a bit of a falling out, so we haven't kept in touch much, but he agreed to take me in while I was in Glasgow. I expected awkwardness, yes, but from the moment I shook his hand something changed. I know it sounds odd, but I swear that's what it was like. I felt as if I could feel the vibrations of his body every time he moved." Henry's voice became distant, thoughtful. "And I am not being metaphorical, either. I could literally feel him. All the time. It was driving my insane. It was like an itch to touch or...something."

Sherlock rolled his eyes.

"Don't roll your eyes at me, Mr Holmes." The urgency has all but disappeared from Henry's voice, leaving only absolute conviction. "It was one of the most intense experiences of my life."

"Have you got any of the sugar with you now?"

"Yes. And I'll leave it with you, Mr Holmes, but a friend of mine who works in a research lab couldn't find anything unusual with it, so..." Henry let the words peter out, assessing correctly that finishing the sentence would not win him any points with Sherlock.

"And you are sure no romantic inclination existed in you prior to this meeting?"

"If you are asking if I never had feelings for Christopher, then I can't say that I haven't. But I had very good reasons not to act on any sort of feelings. In fact, acting on them was the most reckless thing I could have thought of. I assure you, Mr Holmes, what I have done, I have not done voluntarily."

Sherlock levelled him with a stare. "And you believe you were...under influence? Of a love potion? Why not a drug? Maybe your drink was spiked."

"It couldn't have been. I had had nothing to eat or drink on the road, only at home. And the strange feeling started before I even had a glass of water in the restaurant. Besides, as I said, I had my food and water tested. There was nothing that could explain this."

The two men sat in silence for a few moments, Henry's gaze locked on the window, while Sherlock observed his client, before Henry spoke up again, his voice soft in the dusty air of the flat.

"Can you imagine it?" he asked, looking back to Sherlock. "The possibilities of it?"

Sherlock feigned nonchalance, and shrugged.

"It would not work. Not in the long run, anyway, not without a constant renewal of the dosage."

"What makes you say that, Mr Holmes?"

"I assume that the 'potion' is really just a clever cocktail of substances that are usually the basis of such feelings as closeness, attraction, and bonding. Oxytocine, serotonin, possibly some pheromones. Love is nothing but a simple disturbance of brain chemistry. It's perfectly replicable through chemical manipulation. Although I must admit, it is interesting that you found a way to administer it in form of powder instead of injections."

Henry cocked his head to the side, looking vaguely disappointed.

"A man with such a mind, and you cannot, even for a minute, consider that there might just be such thing as a love potion, can you, Mr Holmes?"

"I can consider it. I have. And I have dismissed such a ridiculous notion."

Sherlock counted on the fact that Henry would assume he was dismissing the existence of magic, altogether. It was the logical thing to do. But that didn't necessarily make it true. A childhood spent around Mycroft taught Sherlock that half-truths were the safest truths and the cleverest lies. They catered to the conflicting nature of people to be both suspicious and mentally inert and satisfied their superficial doubt while allowing them to rest comfortably in the belief that no more prodding was necessary. People liked to think themselves insightful, and the brain was trained to fill in the missing information. So Sherlock offered chosen nuggets of the truth, leaving out other ones, and let the lesser brains do their thing. Hopefully, Henry Knight would not deviate from the general populum.

Because the full truth was that there was no such thing as a love potion, but that did not mean there was no such thing as magic. Only, magic was not what most people imagined. There were no such things as wands or flying broomsticks. Magic was simply energy manipulated in a different manner. Like shattering white light into a rainbow using a prism, magic was the energy of things refined, transformed, redirected. Some of the old customs, such as burning herbs or chanting incantations were simple physics, really, using heat and sound to mold certain forms of energy. Not many people knew about magic, and even less were left in the world with the capacity to practice it. Theoretically, anyone could do it. Practically, it took a lot of will power, endurance and sheer wits to dabble into such things. That, of course, meant that Sherlock had been practicing magic since the age of 7, much at his parents chagrin. Mycroft, damn him, had been at it as early as age 5.

The rules of magic were numerous and varied in complexity, depending on the spell. Commanding light was the easiest, followed by heat and then pressure, which was why most mages could set things on fire, make themselves invisible, or fly. Sherlock liked flying although he rarely ever got the chance to do it, and was a master of camouflage. Such energies conformed to a set of laws and rules that made them predictable and stable. Paradoxically, the more rules there were about manipulation the energy, the easier the spells. The more abstract energies of things such as thoughts were far more demanding, simply because they tended to deviate more from the rules of the norm. That too depended – controlling the will of lower classes of the animal kingdom was moderately easy, while birds and mammals posed a serious challenge. Humans were almost never even considered, apart from a few selected incidents throughout history.

But there were energies far too great and powerful to ever be contained. Contrary to common belief, life energy was not the greatest of them. Using magic to kill was frowned upon, and dangerous for the person doing the killing, but it was possible. It was a simple matter of opposites cancelling each other out, like water putting out fire. In order to kill a living being using magic, the sorcerer or witch had to conjure enough of the energy opposite of the one they wanted to extinguish, which was to say that in order to end a life, they had to be able to contain, for a short period of time, enough death in themselves to match the amount of life energy they aimed to destroy, before releasing it on their target. Killing insects, plant, and smaller animals was dangerous, uncomfortable, but not impossible. Killing people, on the other hand, was bordering on self-destruction most of the time.

But even life conformed to a loose set of rules, as did the human psyche. Human emotions, however presented an energy that never conformed, and which, if tempered with, became distorted, rotten, and dangerously volatile. Attempting to manipulate it would lead to the destruction of the sorcerer or witch. Which was why there was no such thing as love potions.

Of course, Sherlock could not well tell Henry that. But he had to tell him something. So he told him the truth. Just not that particular truth.

"People don't really fall in love with other people. Not at first at least. All infatuation is, at its core, narcissistic. People fall in love with mirrors, with the disfigured reflections of themselves, because they see themselves through the eyes of someone blind to their faults. They fall in love with the admiration, the worship, the possibility of deluding themselves with this upgraded image of themselves. In such a state irrationality intensifies and people are prone to all sorts of ridiculous behaviours. I dismiss the notion of a love potion simple because all such behaviour is simply and completely explained by the chemical defect found in people who claim to be in love. The chemistry of love is highly destructive, but there is nothing supernatural about it."

"Perhaps. But will you still take my case?" Henry was unrelenting in a manner typical of people who grew more certain of being right the more times they were told they were wrong.

"What case? There is no case. I will analyse the sugar and prove to you that you probably contracted a fungal infection that affected your perception." Sherlock replied haughtily.

"Alright. They didn't find anything at Baskerville, but I hope you have better luck. If you change your mind, I am fully prepared to pay your trip to Dartmoor, to investigate."

Sherlock's head snapped up, his focus sharpening. "Did you say Baskerville?"

Henry looked slightly spooked, but nodded hesitantly. "Yes. The friend I told you about, the one who analysed my food and water for me, he works in Baskerville."

In an instant, Sherlock was on his feet, crowding Henry out of the chair and onto the landing outside the door.

"Mr Knight, expect me and my associate in Dartmoor by tomorrow morning. Now, if you'll excuse me, I have to pack."

Henry looked properly bewildered. "What? Oh...yes, ok. Tomorrow, then. Should I e-mail you the address?"

"Yes, that would be perfect. Good day, Mr Knight." And with that, Sherlock closed the door to the flat, leaving a thoroughly confused Henry to walk out the building and head towards the tube station nearby.

Back at the flat, Sherlock paced the length of the den before settling down in his chair, elbows on knees, palms pressed together under his chin. Baskerville. Mycroft tried his best to keep Sherlock as far from the research base as possible. Deep in the middle of the sleepy English countryside, experiments were being conducted with some of the most dangerous types of magic known to man. Sherlock had been waiting for an opportunity to snoop around for ages.

The tell-tale beat of footsteps echoed from the stairs. John was home. Excellent.

"You need to pack. We're going to Devon." Sherlock announce as soon as John walked through the door.

"Devon? Why?" John asked, looking at Sherlock in confusion, but with undeniable amusement. No, no...not amusement...something else... Sherlock ignored the itch under his skin that strangely returned, deciding it was simply there because all the smoke from Henry's cigarettes had long dispersed. He swooped past John towards his room, turning on his heel to cast John a grin.

"For a case, John!"