Disclaimer: I do not own Sherlock and co. They belong to BBC and Moffat.

Three:

A Study in Potions

When Sherlock had asked him if he wanted to help solve a case, John had thought that they would actually do some chasing, or at least spy on the suspect from a safe distance. It had not crossed his mind that the first thing they would do was enter one of the more sophisticated restaurants in the outskirts of Hogsmeade. To get dinner.

John had spent the last five minutes staring at Sherlock who sat opposite him, barely even glancing at the menu that had been handed to them by a young wizard. He was fiddling with his phone (it looked like a normal Muggle phone but John knew that it had been bewitched as technology didn't work in the presence of so much magic) and he had not glanced in John's direction even once. John was beginning to regret coming along when a jovial, heavy-set man walked to their table.

"Sherlock!" the man greeted. He gave them pats on their shoulders. John nearly smacked his face on the table from the force. "It's so good to see you again. And you brought a date!"

John flushed. Oh god, he thought, this does look like a date, doesn't it? They were seated in a corner booth in a fancy restaurant that John guessed was the adult version of Maddam Puddifoot's. The wizard waiting on them had even placed a candle in the middle of the table, the one that John had put out as soon as it had been set down. "I'm not his date," he said to the man but it fell on deaf ears.

"John, Angelo. Angelo, John," Sherlock said lazily.

"Good man, our Sherlock," Angelo, who John realized was the proprietor, said, beaming, "Some Aurors had pegged me for a murder a year ago but my boy Sherlock here proved them wrong. Would have gone to Azkaban if he hadn't shown up in his school uniform and all. This boy here proved me innocent."

"Angelo's alibi was that he was trading in the black market on the same day of the murder. You did go to Azkaban, Angelo."

"Only for a few hours," Angelo replied, not at all put off by Sherlock's misdemeanour. "Food's on the house as usual, Sherlock. For you and your date."

"Not his date," John repeated but Angelo had already gone away. He turned to Sherlock and gave him a 'can you believe this?' look, but his companion didn't even acknowledge him. John sighed and waited for the food to arrive. It came after three minutes, pasta and clam chowder and something that was probably Greek. John dug in, only too happy to fill his empty stomach. Sherlock, however, didn't touch his food.

"Aren't you going to eat?"

"I'm on a case, John. Digestion slows down my thoughts." Sherlock's eyes skimmed John's face briefly before they dropped to his phone. John wondered who he was texting. A Muggle? Another wizard with a phone like his? The latter seemed more likely.

"So…um…" Blimey, why did he feel so nervous? Was it the atmosphere of the place? It really wasn't comforting to know that people thought he and Sherlock were on a date right now. Not that Sherlock was horrible. Rude, yes, but well, even John could see he was good-looking. But he was straight as a…as a…well, straight as the straightest thing in the world, whatever that was. He probably only found Sherlock attractive because he had some Veela in him.

"As a matter of fact, I do," Sherlock replied when John asked, eyes still on that damn phone. "One-eight, inherited from my mother. Very few male children born with a Veela heritage exhibit the ability to seduce without too much effort (here, John flushed). I'm one of those few. You've seen my brother, of course. He takes after Father more but Mycroft doesn't need this trait to manipulate someone."

"Ah, I uh, guessed since you look…er, like you have it." Any idiot could see that, John thought. Sherlock was tall, willowy, had those weird eyes, and was naturally graceful. "Your girlfriend must brag about you a lot. I mean, since it's so rare and all."

"Girlfriend? Ugh, not my area."

Oh. Oh. This wasn't disturbing. No, of course not. John's sister was a lesbian. Sherlock was gay, so what? "You have a boyfriend, then?" A small voice in the back of John's mind was desperately telling him to shut up. It got louder when Sherlock's eyes narrowed. Thinking that John might have offended him, he quickly said, "I mean, it's fine! Fine, it's all fine. Er…"

"I know it's fine. Boyfriend, girlfriend, not my area, John. I don't do relationships." Then, he frowned at John for a while, making the other boy feel very uncomfortable. John cleared his throat. Change of topic, he thought.

"So about joining the Quidditch team…That's just for the case, right?"

"Oh, yes. Sports do not interest me."

"So you're not going to play this year?" John couldn't suppress the hopeful note in his voice. If Sherlock didn't play, Slytherin was screwed. He'd heard about the others who'd tried to win the position and they hadn't been very good.

Sherlock quirked an eyebrow at him, a smirk playing on his lips. "Why, it seems you're threatened by me, John," he said, his voice teasing. "I do not hold any interest in sports. I don't care about Quidditch at all. But it doesn't mean I won't try it. I've never played a game before and playing one match will not only help me see what all the fuss is about, but will also help me with my study on human behaviour—though said humans are imbeciles. I'm not staying after that, though, as not only do I hate flying—don't look at me like that. I know I fly well but that's because I've been doing so since I was a child. That does not mean I enjoy it. Anyway, what's our first game this year? Oh yes, Slytherin versus Gryffindor." He paused, then grinned at John evilly. "It could be interesting."

He's trying to rile me up, John thought. "Didn't think you were on the competitive side."

"That's because you rarely think."

John gritted his teeth. Right. Sherlock was an arse. But he was also an arse who was providing John a free meal. Also, if John walked out now, he'd have no place to go. It was already past curfew and the Hogwarts gates were now closed. The only way to enter was to wake up Mortimer Filch, and John would rather get eaten by wild beasts in the Forbidden Forest than to cross the grouchy old man. Sherlock knew a way in, of course. He'd obviously done this before. John would just have to sit back and watch Sherlock in his element.

I'm going to kill him.

John's lungs were threatening to burst. He finally allowed himself to stop running, his exhaustion getting to him. Panting, he leaned against a brick wall and waited for his heart to stop racing. Where was Sherlock, damn it? John was not sure if he was dead or not but if he were alive, well, John wouldn't hesitate to strangle him.

He had no idea what had happened. One moment they were eating and the next thing John knew, Sherlock had gotten up and gone outside. John had watched him hail a Knight Bus from where he sat. That was all. He hadn't seen Sherlock get assaulted but something told John that he was in mortal danger. He had tried to reason with himself that Sherlock was fine, that this was part of his plan. But there was a nagging feeling in John's chest that wouldn't die, which was how he found himself tearing down Hogsmeade, wondering where the hell Sherlock had gone off to. He'd taken the Knight Bus meaning he could be anywhere by now. He could even be in Surrey.

Wrong, wrong, wrong, Sherlock, danger. The words tumbled in John's mind. But where to look? Sherlock hadn't given any indication to where he might be. He had just sat there, amiable until he got this strange look on his face that John had associated with realization. He'd realized something—who the suspect was, maybe?

John was definitely going to kill him.

He could turn around. Go to an inn, maybe, and send an owl to Bill and Mike to tell them where he spent the night. This was the safest thing to do but John hated playing safe. And he couldn't do it when he knew that Sherlock might be lying unconscious somewhere.

A loud screech interrupted his thoughts. Looking up, John saw that a sleek black car had stopped before him. The door opened and a pretty woman holding what John guess was a Blackberry stepped out. "Mr Watson," she said, her eyes still glued to the screen, "my employer would like to speak to you."

When John didn't budge, she huffed impatiently then said, "I take it you're out looking for the younger Mr Holmes. You're wasting precious time standing in the curb."

The younger Mr Holmes? Oh. Mycroft. John blinked, dazed, then allowed himself to be pushed in the car. As expected, the interior was bewitched to look like a sitting room. John took a seat and found himself face to face with Mycroft Holmes.

Mycroft had changed little since he graduated from Hogwarts four years ago. He had grown a little soft around the waist and his hair was shorter but other than those things, he remained the imposing figure that had leered over John when he was still a First Year.

"Well, well, John Watson, it is a pleasure to see you once more." The man's smile was insincere, mocking. It was disconcerting. "Pray tell me how your sister is. Still causing trouble?"

John shrugged. He didn't like Mycroft with his creepy smiles and pompous air. "She's fine."

"Yes, I'd say so as well since you were able to leave her long enough to go gallivanting with my dear brother. Tell me, John, what is your relationship with Sherlock?"

"We're not really close."

"And yet you willingly accepted his offer to take a case and have a romantic dinner with him. Must I inform Mummy of an oncoming wedding?"

John flushed, though if it were from anger or embarrassment, he couldn't really tell. He glared at Mycroft who simply smiled back. "He's in danger, I think," John muttered, looking away, "Sherlock, I mean."

"My brother is always in danger." There was something more to that and when John peered at Mycroft's face, he saw a tense weariness that had not been there before. But it was gone too quickly and John wondered if he had imagined it. "Where do you think Sherlock is, John?"

"Knockturn Alley." The answer came to him automatically and saying it out loud told John he'd hit the nail on the head. Mycroft's smile grew a little more so that it wasn't just an imperceptible twitch of the corners of his lips.

"Hippogriff feather, isn't it?"

"Sorry?"

"Your wand core. Hippogriff feather encased in oak, most likely. Uncommon but not extremely rare. Can only be mastered by a very patient wizard like yourself. A powerful wand. Ollivanders, of course." John stared at him confusedly while Mycroft chuckled. "It explains so much. Priori Fraternitas."

"What's that?"

"Do your research, John." Then to John's surprise, the doors opened. The familiar smell of Diagon Alley entered the car. "This is where I leave you. I'm afraid you'll have to walk the rest of the way to get to Knockturn Alley, but it isn't far.

"You're not coming?"

"My brother would rather kill himself than let me rescue him. No, John, the night is yours." John stepped out. He looked over his shoulder at Mycroft. "Good luck, John," he said. The doors closed and John watched as the car sped off, disappearing in the night. The streets were already empty and the only ones that could see him were the gas lamps that cast an eerie yellow glow over the place. Wand out, John ran the rest of the way to Knockturn Alley.

"It's obvious, really."

The man looked up from the flasks on the table and eyed him amusedly. He wiped his wet hands on his trousers and walked to where Sherlock sat. Walks with a slight limp, muscle pain, no permanent injury, recovering from a sprain. Sherlock moved to the man's face. Late forties, bland, scar on temple.

"Tell me," the man said. Hoarse voice, yellowed teeth, chain smoker, no scent of smoke, hands twitching, decided to quite a few days ago. "How is it obvious?"

"Transportation. Not all of your customers are off age meaning Apparition isn't possible. Flying can be done but it would cause suspicion and it would be hard to bring back potions when on a broomstick. Portkeys cause suspicion as well. Other magical articles that are used for transportation can only be found in Dervish and Banges but since the Potter Age, shops like that are heavily guarded by the Ministry. What's the one thing that can't be detected easily due to speed? The Knight Bus. The main purpose of The Knight Bus is to bring students from one place to the other so it wouldn't cause alarm if a multitude of students ride it. Why Knockturn Alley? The Ministry guards it but not the shops closer to Diagon Alley. This is a perfume shop and one that doesn't do very well because you're a driver at night. The potion is sold in perfume bottles which masks the original scent. It is given to females as a present and once sprayed it makes them lustful, but since it is only sprayed and not ingested, it doesn't have the full effect. Stronger minds are able to resist and can acknowledge what is happening to them. That's your mistake there."

The man chuckled. Hope, Sherlock remembered. He had told him when Sherlock rode the Knight Bus alone. It did not really matter. He would forget the name in the morning.

"You're a smart boy, Mr Holmes," Hope said. "He was right about you."

"He?"

"You've got a fan. Well, fans. But I work for just the one."

Steady voice, eyes focused, not lying. "This fan has a name, of course."

"Yes."

"You're going to tell me." Hands in pockets, small object inside, two. "But you have a proposition."

Hope grinned, showing all of his teeth. He extracted his hands from the pockets of his coat and laid out two small bottles. Inside each was a thick black liquid. Sherlock unscrewed one and took a sniff. No scent greeted him.

"Black Draught, no antidote, five seconds until death, enough time to say a name," Sherlock muttered, putting the bottle down once more. "But one's safe."

"Good, good."

"And if I don't drink?"

A wand was pulled out. Eleven inches, holly, must be unicorn hair. Sherlock rolled his eyes. Typical."You have a wand as well, Mr Holmes," Hope told him. Sherlock reached for his own wand and laid it on the table. He did not miss the way Hope's eyes stared at it hungrily, did not dismiss the anxiety in them.

"But you're not going to use it. You like a challenge don't you?"

"You are aware that I don't need a wand to blast you to the other side of the room."

"Oh yes. But the Ministry won't like that, won't they? You're too strong for your own good without a wand to direct your magic. Might lose control and end up not just killing me, but others as well. Azkaban ain't a good place for someone like you."

"You've done your research."

"Your fan's very persistent."

Sherlock sighed and took his wand back. Hope did not. He pointed it at Sherlock, aimed it at his chest. "You know they still won't love you," he told him. Hope's eyes narrowed. "You're doing this because you need the money to win your children back from your wife who comes from a well-to-do family. I saw the picture on the dashboard. It's not going to work."

Anger, hurt. Hope gritted his teeth. "Less talking, more guessing," he growled. Then he smiled. "Come now. Smart boy like you can cheat death, can't you? Two potions, completely identical. Can you pull it off, Mr Holmes?"

Sherlock stared at him then at the bottles. Identical in appearance, but seemingly so. There was always a give-away. Sherlock weighed each bottle in his hands. "This one," he said, pushing the other bottle toward Hope. Hope smiled. Strained, nervous, not at all confident. Now that Sherlock had reversed the position of the bottles countless of times, Hope was no longer sure which was the poison.

You can die, you know. His wand seemed to burn in his pocket. Absent-mindedly, he brushed his fingers against it.

No scent, very dark, consistency of condensed milk.

He looked at Hope who stared back.

You won't die. You picked the right bottle.

But if you do, you're not coming back as a ghost. You're no coward.

But then you won't be able to continue solving Father's death.

He blinked. You left John in the restaurant. Idiot!

Sherlock lifted the bottle to his mouth. Hope did the same. Cold. The rim brushed against his lips, wetting it slightly.

Sweet.

"Everte Statum!"

Sherlock spat the small bit of potion that had entered his mouth at the same time as Hope was thrown backwards. Something warm and wet splattered his front, and the metallic scent of blood entered his nostrils. "Oh shit oh shit oh shit," someone stammered beside him.

"Wh—"

"You idiot!" He was roughly pulled from the chair. Sherlock wiped the scant drops blood off his face and stared. An ashen-faced John glared back at him. John's here.

Mycroft's doing.

"That was poison, wasn't it? Shit, I almost forgot Alohomora. If I hadn't remembered it and unlocked that door in time—I didn't kill someone for you for nothing!"

Sherlock followed John's gaze to where to Hope lay. A large jar lying on top of the shelf behind them had crashed on him and bits of glass impaled his skin. The bottle in his hand was also crushed and the dark liquid oozing out of it hissed, burning the carpeting. Hope was wheezing but it would only be a matter of time before death caught up with him.

"The name, what is it?" Sherlock demanded, pushing past John.

Hope coughed. Blood bubbled from his mouth and dribbled down his chin.

"The name!" Sherlock yelled. He would have grabbed Hope but the shards of glass told him to back off. "You're dying but I still have time to hurt you!" He put his foot down the man's stomach which had sustained the most injury. A high-pitched squeal escaped Hope, drowning out John's cries.

"Sherlock, what are you doing?!"

"The name! Say it!"

"MORIARTY!" Hope screamed before his head dropped, his blank eyes staring straight ahead.

"Don't smile," John muttered. "That's not decent."

"You killed someone and you talk of decency." Moriarty. Never heard of it. Must do research.

"I didn't mean to! I only meant to knock him backwards." John paled even more. "Am I going to Azkaban?"

"It was self-defence." Sherlock whipped his phone out. "I'll explain everything to the Aurors."

The Aurors arrived five minutes later, pouring in the room in twos and threes. A man who looked remarkably like Lestrade stared at Hope then at the two boys for one moment before throwing his hands up. "I told you a million times, Sherlock, no going after the criminals! I'm risking enough by letting you solve cold cases."

Next to him, Sherlock rolled his eyes. There was a drop of blood on his temple that the cleaning spell John had cast on him must have missed. "You're too slow," he complained.

"Well, you should be in school!"

This exchange went on for quite a while. John didn't even know that he had fallen asleep until someone was shaking him awake. A woman with bright green eyes smiled down at him. "Let's get you back to school, love," she said as she ushered him inside another car, this one smaller than Mycroft's. Sherlock was already seated, looking quite angry. It had little effect because of the garish orange blanket wrapped around his thin frame.

"Go to bed," Sherlock muttered when they reached their destination. John blinked at him blearily. "Headmaster Shacklebolt is still awake. Apparently, I have some explaining to do."

"A lot, actually," the Auror who'd followed them said. She bid John goodnight then walked down the hall with Sherlock who trailed behind.

The Common Room was empty but for one First Year who had fallen asleep in front of the empty fireplace. John climbed to his room, his steps languid now that the adrenaline rush had left his body. "John?" Bill muttered when he opened the door. He lifted his head slightly and peered at him. "Where've you been?"

Where haven't I been? John didn't bother to answer. He climbed in bed and let sleep take him.

It was in the Daily Prophet the next morning. John read the article as he and Bill walked to the Great Hall. "What a tosser," Bill said as he read over John's shoulder. John muttered an agreement. There was no mention that there had been two underage boys present in the crime scene.

The Great Hall was packed with students, some of whom had just returned from their homes. They were all talking about the murder in Knockturn Alley. A few of the girls looked aghast and John assumed that these were the same girls that had fallen victim to the scam Hope had made. He also noticed that some students, most of whom were Slytherins, were not present. John wondered what Sherlock and Headmaster Shacklebolt had talked about last night.

Speaking of the boy genius, John found him in his usual spot, sitting far away from the others. A cup of tea sat in front of him as well as a thick book but nothing else. "You go ahead, Bill," he said, and ignoring Bill's protests, he made his way to the Slytherin table.

"We made front page," John said when he reached him, his voice lowered so others wouldn't overhear. They were already attracting attention. Some Slytherins were glaring at John while the Ravenclaws nearby looked surprised to see a Gryffindor there, especially one that was talking to Sherlock Holmes. John ignored them.

Sherlock looked a little surprised to see him. His brows were furrowed and he pursed his lips. He opened his mouth to say something but John cut him off, "Look, you don't accidentally kill someone and pretend that nothing happened." The sane part of John asked him why he was okay with this. He had killed a man last night and he felt nothing but exhilaration. He should be worried, but he wasn't. He felt…normal.

"You're saying I owe you then." Sherlock dropped his eyes to his book, scowl in place. "If it's money you want I can provide you with plenty. Say how much and I'll give it to you."

John's gut twisted at that. "No," he said, making Sherlock look up once more. "I'm saying that…well, repeating that you're okay, Sherlock."

"Oh." Sherlock looked even more confused. He's never had a friend before. John winced inwardly then chided the sympathy that was crawling into his mind. No sympathy, he reminded himself.

"Mind if I sit down?"

"They do." Sherlock motioned to the rest of the Slytherins who were doing their best to repel John with disapproving glares. "But," Sherlock began, smiling slightly, "they're not important."

Laughing, John sat down. There, he spent the rest of the morning forcing Sherlock to eat something while at the same time ignoring the looks and whispers from the others.