"I'm going to the library," Sherlock said as they left Greenhouse Six that afternoon.

"Nope," John said.

"What?"

"You're not." John grinned at the look of confusion on Sherlock's face. "You're coming with me."

Sherlock frowned. "Is something wrong? Only this morning you assured me you were feeling well enough to attend your lessons without me. And you've been rather cheerful all day, considering what you've gone through." He paused, lips pursed in thought. "Perhaps it is the dusk, reminding you of the moment when you lost consciousness and making you feel less safe. However, John, I assure you..."

"Could you shut up for a moment?" John asked, amused. "It's touching how worried you are about my well-being, but I really am fine. You just have somewhere else to go."

"Oh?" Sherlock gave him a searching look. "And wherever might that be?"

"My common room," John said.

"So... you do want my company?" Sherlock asked.

"Do I ever not want your company?" John rolled his eyes. "This isn't about me. It's about the party."

"What party?" Sherlock looked like John had gone crazy. "John, you know perfectly well I don't do parties..."

"Yeah, except when they're celebrating your own birthday."

"You... I..." Sherlock was sputtering in indignation. "I don't celebrate my birthday!"

"Well, you do now!"

Sherlock groaned loudly. "John... Please don't tell me there will be other people. Or music. Or dancing, for heaven's sake. I need to do research, find out who Moriarty is and how we can get to him..."

John sighed, slightly disappointed, but to be fair he had known Sherlock wouldn't be as delighted at the prospect of a party as he was. "You can't let that man ruin your seventeenth birthday, Sherlock. Or any other day."

"I'm not planning to let him do that," Sherlock countered. "That's why I want to stop him as soon as possible."

"I... I get that," John said, taking Sherlock's hand. "And I agree, really, but... They'll all be coming down to the common room anyway. I invited them days ago and... I didn't feel like blowing it all off, so..."

"It's fine," Sherlock said, but then he frowned again. "They'll all be coming? Who will?"

John shrugged. "All your friends?"

"My friends?" Sherlock repeated. "So it'll be just you after all?"

"Don't be an idiot," John said, rolling his eyes.

The Hufflepuff common room was in fact rather crowded when they entered. And it became even more so after a few minutes, when Bill let in a bunch of people from the other Houses.

"Happy birthday!" he told Sherlock, a skip in his step as he walked over and grinned widely. "Brilliant plan of John to adopt you as a Hufflepuff. We haven't had a proper birthday party in a month or more!"

Sherlock snorted. "So glad to be of use."

"We better go fetch the food, though, John," Bill said. "Before they start eating first-years..."

"Coming!" John stood up and, feeling exuberant, dropped a kiss on Sherlock's hair. "I'll be right back."

"I'd hope you weren't planning to leave me here," Sherlock replied, actually looking a little afraid at the throng of people.

When John, Bill and Mike returned from the kitchen with their arms full of nibbles, cakes and bottles of pumpkin juice, a dark-haired girl was talking animatedly with Sherlock. As soon as everything stood on the tables – which were attacked immediately – John wormed his way past some Gryffindor Quidditch players and back to Sherlock, holding a plate.

"Got you a bit of that chocolate cake you love," he said, beaming at Sherlock as he handed it to him.

"Oh. Thank you." Sherlock smiled at him and John felt slightly giddy. He really did want to make this a memorable day for Sherlock, in spite of threats and fears. He deserved it.

The dark-haired girl cleared her throat.

"Right," John said, looking up from Sherlock. "Who are you, then? Did we actually invite you?"

She laughed. "Oh, you wouldn't want to miss me at a party. Irene Adler." She held out an elegant hand for John to shake.

"John Watson. Nice to meet you," John said.

"She's in Slytherin, the year above us," Sherlock explained.

"I took the liberty of bringing Kate, my girlfriend," Irene said, reaching out and somehow pulling a blonde, taller girl from the crowd. "I believe you have met."

John nodded at the Slytherin Chaser. "Sorry about that Bludger last year."

"Don't worry about it," Kate said, smiling. "It's part of the game. And I'm all for games." She winked at Irene and John felt he should look away from them very quickly.

"Well... I'm dying to check out those almond cakes," Irene said. "Congratulations, Sherlock." She leaned over Sherlock's chair and landed two resounding kisses on his cheeks, leaving John to stare at her in shock.

"Wow, boys," a voice said behind him when Irene and Kate had turned to the food table, and John still hadn't remembered how to close his mouth. "I didn't know you were into all that."

Mary Morstan joined them with a very... evil... grin.

"Into what?" John asked.

"You know... Irene..." She giggled. "I'm not judging you, but it is a tad unexpected."

"I have no idea what you are talking about," John said.

"No?" Mary said. "Oh... I thought people outside of Slytherin knew about her too. She provides a rather... unusual... kind of entertainment. For those who lust after... pain... power plays... all that kind of stuff."

Not only did John's mouth return to its open state, it also felt like his eyes were going to roll out of his head. "She... You're kidding, aren't you?"

"She isn't," Sherlock said, his face frustratingly expressionless.

"But... how... She can't possibly do that here at Hogwarts!"

Mary snorted. "What, because the teachers would notice? Don't be silly, John. Apparently there are rooms in the castle that are well-known for this kind of thing among the oldest students."

"But... She has a girlfriend!" John protested.

"And they are in an open relationship." Mary rolled her eyes. "Really, Sherlock, how can you stand him? Happy birthday, by the way."

"Thanks. I don't know, sometimes." Sherlock smiled up at John and actually winked.

"But... No, I'm not getting over this," John said. "They have sex? At Hogwarts?"

"I had no idea you were so innocent," Mary said, clearly delighted. "Poor Sherlock..."

"What better place for her business than a school full of sexually frustrated teenagers, willing to experiment?" Sherlock pointed out. "She must earn quite a lot of money."

"She's paid for it?" John cried out, and then realised that maybe he should keep his voice down if he didn't want Irene to hear him.

"Oh, and not just in money," Mary said. "It's really quite brilliant. I mean, I wouldn't want to do it myself, but I sure admire the idea. The things she must know..."

"Know?" John repeated, starting to get a little annoyed how he seemed to be behind on this whole conversation.

"Well, yes," Mary said. "She knows what everyone likes. And she's probably come across quite a lot of other secrets that way... And think about the blackmail possibilities."

John raised an eyebrow at her. "So that's something you find admirable."

"It's clever," Mary insisted.

"It is, isn't it?" Sherlock said, sounding rather absent and looking over to where Irene was laughing at something Bill Murray had just said. John had the odd urge to drag Bill away from her and inform him how dangerous she was. But maybe he was actually up for a bit of that sort of danger. And this really wasn't a train of thought John wanted to follow about one of his friends, so instead he focused on Sherlock.

"You're looking far too interested," he informed him.

"Hmm."

"There are pancakes!" Mary suddenly exclaimed, and before John knew it, she had disappeared, leaving him with a non-responsive Sherlock.

Knowing that it wasn't much use hanging around if Sherlock was in such a mood, John decided to find other company as well and joined a group of his Quidditch mates.

"Everything alright with him?" Greg Lestrade, the seventh-year Gryffindor Keeper, asked, nodding towards Sherlock.

"Yeah," John said. "I think he just had an idea and I'm not sure I want to know."

The Gryffindor captain, Sebastian Moran, chuckled and a third-year girl, who came by with an almond cake in her hand, actually stopped to look up at his muscled form with large, terrified eyes, which made John laugh too.

"Don't worry, he's not going to bite," John told her, and the girl fled.

"So you're together now?" Greg picked up the conversation again.

John grinned and felt himself blush a little. "Well..."

"Good for you." Greg seemed genuinely happy for them. "I just have one big question..."

"Oh yeah?" John said.

"Why isn't there any music?"

...

"Phew, it's been a long while since I danced this much!" Molly swept the sweat off her forehead as she flopped down in the chair next to John's, slightly out of breath. On the other side of the room, Greg was still staring open-mouthed at the spot where she had been waving her arms around and head-banging just a moment ago.

"Looks like you had a good time," John said, smiling.

"Oh yes, I did," Molly said cheerily. "I hadn't been on a lot of Hufflepuff parties before, you know, but so far everything they say about them seems right."

"Thanks," John said. "Though I hope not everything... In our fourth year there was this very persistent rumour about parties that would be happening in the baths. I didn't dare to wash for a week."

Molly giggled. "I bet that's not actually true. Sherlock would probably start complaining about hygiene and smell after three days."

"He would, wouldn't he?" John laughed and then saw that Sherlock was walking over in their direction, so he waved.

However, the tall boy only took a few steps more, stopping right in front of Irene Adler and actually leaning into her a little.

"Oh, who's she then?" Molly asked. "A friend of Sherlock's?"

"No," John snapped, although he didn't actually know if she was. It would be odd if he'd never told John about her. And yet Sherlock seemed to have known all about Irene's unusual occupation. What if he hadn't mentioned her because he was interested in her services and didn't think John would approve? What if he had made use of them?

"Excuse me, please," John told Molly, and he strode over to Sherlock, making himself taller and broader than usual.

Somehow, in spite of the music and the people chatting around him, all he could hear were Sherlock and Irene's voices.

"So you'll show me," Sherlock was saying to her. "Tonight."

She laughed that infuriating laugh of hers. "Oh, Mr Holmes. Did you really think it'd be so easy? Those documents are my life. What do you think you've done to earn a look at them?"

"A look at what?" John asked, almost pushing over a second-year so he could stand next to Sherlock.

Irene smirked. "Oh, someone is jealous..."

"I have no reason to be," John bit at her. "Do I, Sherlock?"

He fiercely looked up at his boyfriend, whose eyes went wide when they took in his expression. "John..."

"I'd better give you two a moment, I think," Irene mocked. "But just to make it absolutely clear: the answer is no, Sherlock. And don't try to find me. I'll be tied up in a hidden room... Or rather, tying someone up."

"John," Sherlock complained when she'd left. "I'd almost gotten her to open up."

"Open up? Is that what you want her to do?" John snapped.

"What's gotten into you? Why are you all..." Sherlock gestured at John's form.

"I'm not anything." John's voice was almost a growl. "But you heard what Mary said about that girl."

"There's nothing wrong with what she does," Sherlock said, looking a little confused. "There is a demand and she supplies. As Mary said, that's clever."

"Clever, huh?" John said. "Isn't that the greatest good in your book? Got a little crush then?"

Sherlock's eyebrows knitted in puzzlement. Then he grabbed John's elbow and led him to the dormitories.

"What... Sherlock!" John protested, pulling his arm away.

"No. In here." Sherlock opened the door to John's dorm and closed it behind them. "Go on then."

"What am I supposed to do?" John asked, studying Sherlock for any sign of what the meaning was of all this. "Punch you?"

"Is that what this made you want to do?" Sherlock enquired, looking vaguely amused.

"No..." What he wanted was to push Sherlock against the wall and... snog him, John decided. Because if he ended that sentence with where his thoughts actually went, things might turn too disturbing.

"You're jealous," Sherlock explained. "You want to claim me as yours. I'm letting you."

John blinked at him. And then he grabbed Sherlock by the lapels of his robe and smashed their lips together, pulling Sherlock closer, closer, his hands tangling in his hair and sliding over his face and down his shoulders and Sherlock was all his.

He felt infinitely better when they both came up for air.

Sherlock cleared his throat, looking a little winded. "Interesting," he commented.

John was just catching his breath, and slowly his brain was coming back online, replaying what had just happened. "Erm..." he muttered. "Sorry."

Sherlock smirked. "Oh no, it's fine... More than fine."

"I sort of... attacked you," John protested.

"Well... There's a market for that, too. Maybe you could start your own business."

John glared at him.

"However, John, I must admit I'd prefer if you don't," Sherlock continued. "My possessive streak may not go as far as yours, but to be fair I would be disappointed if this grade of affection were to be shared with other people. At least for now."

"For now?" John growled. And then burst out in giggles because he'd realised how that sounded.

Sherlock joined in, looking almost triumphant. "I had no idea you were such a caveman."

"Oi," John said, still laughing. "Seriously though... What was all that about? What precious possession of Irene's did you want to see? Her whips?"

Sherlock snorted. "I doubt she'd refer to those as 'documents'. No, this is quite interesting, in fact. I think that, unknowingly, Mary put me on an interesting trail."

"Do you think those documents have anything to do with Moriarty?" John asked, his eyes widening.

"Well, perhaps not directly. As long as she won't show them to me, I can only speculate," Sherlock answered. "But remember what Mycroft said about the leader of that smuggling gang. She received information on businesses, but we know that Moriarty has a lot on Hogwarts, too. It didn't strike me before, but Irene is in the perfect position to provide him with that."

John frowned. "It doesn't explain how he knew that you'd seen the message in the Daily Prophet's articles."

"True," Sherlock admitted, "but I doubt that he'd only have one person on his side, anyway. If Irene chooses to sell to him, I have no doubt that he has access to secrets that fit into a bigger picture."

John nodded. "Shame she doesn't want to talk to you."

"Oh, I'll think of something," Sherlock said, and he chuckled as John raised his eyebrows. "Something that doesn't involve her services. But John... I really should thank you. Throwing a birthday party wasn't as ridiculous an idea by far as I'd thought before. This could be a massive break-through."

John smirked. "Thanks. And while we're here..." He turned around and dove into the trunk at his bed end to pull out a wrapped parcel. "Happy birthday."

Sherlock took it and glanced at it. "A book, John? Really?"

"Well, I don't want a repeat of last year..." Admittedly, Sherlock had been fond of the Clabbert brain John had gotten him. So fond that he'd brought it to dinner one evening and had taken it out of the jar, putting it on the Hufflepuff table and poking it around, claiming he was studying it, while John had been trying to eat. From that point on he had resolved to be more careful in his choice of gifts for Sherlock.

Sherlock tore the wrapping paper from the book and then read its title. 'Magical Murder and Misdemeanour - an account of 56 unsolved mysteries in the last 7 centuries.'

"Oh," he said. "That's... That's actually..."

John snorted. "Are you surprised that I know you well enough to choose the perfect gift?"

"Yes," Sherlock answered, looking up with a very bright look in his eyes. "You never stop surprising me."

John chuckled. "You're welcome."

...

By the time John was saying goodbye to their last non-Hufflepuff guests, Sherlock was curled up in one of the chairs with his new book.

"I thought you couldn't party because you wanted to work," John remarked as he perched on his armrest.

"This is ridiculous," Sherlock muttered in answer, gesturing at the book. "How could they not see that it was the wife? She poisoned his tea and vanished the body. The motive is clear, too. She wanted to elope with that mysterious letter-writer they suspected but never found. Who was a woman, by the way. I wonder if the murdering wife cared when she found out."

"Oh," John said. "That's only 55 unsolved mysteries now, then."

"54, actually," Sherlock said. "But the other six cases I've read so far were far more challenging. I'll need to gather more data to break through those."

"Good to hear it's not boring you just yet." John smiled. "But what about our case?"

"Oh, I know what to do." Sherlock closed the book and put it on the table, then turned towards John. "I just figured I might as well kill the time reading. You see, Moriarty is probably a dead end. We'll need to focus on his associates to get to him. And Irene was very eager to stress that she will be busy tonight, but considering what she'll be doing, I doubt she can take the documents with her. For all that it's 'her life', it may be quite easy to get a good look at them."

John frowned. "What are you planning?"

"Breaking into her dormitory," Sherlock said, grinning. "Oh, I know," he continued as John wanted to open his mouth, "she's not the only one sleeping there. But I'll think of something to clear the room."

"That's not actually your biggest issue," John said. "The girls' dormitories are protected against boys, you know. Loud alarms, sliding stairs... At least it's like that in the Gryffindor tower, but I'm sure the other dorms have security measures too."

Sherlock raised an eyebrow.

"I... I found out when I was seeing Sarah Sawyer," John mumbled, blushing. "In our fourth year. You know it wasn't... That I didn't..."

"Yes, alright." Sherlock smirked, apparently feeling that John had struggled long enough. "But really, John. In any other circumstance I'd be disappointed that you let yourself be stopped by such simple magic."

John frowned. "It's kind of hard to stop a staircase from turning into a slide while you're already standing on it, you know!"

"But the protection can be switched off," Sherlock said. "Obviously. Otherwise they'd be in a lot of trouble every time they accepted a student of non-binary gender, and I doubt Professor Bell would let that happen."

"Oh," John said. "I suppose... I hadn't thought of that."

"No, the hard part will be finding a distraction that is subtle enough not to raise any kind of suspicion, but striking enough to let them all come out. Unless I simply go for the Dungbomb approach..."

"Won't that girlfriend of hers, Kate, be suspicious anyway if she sees you?" John asked. "Maybe you should ask someone else to get them out of there. You could ask Mary, she'll probably help." He pointed at the blond girl who was one of the last Slytherins in the common room, peeling the last pancake from the plate that had been holding a four feet high stack.

"Excellent," Sherlock said, nodding. "You ask her – she'll react better to you than to me. And then we'll just have to wait until Irene is off to her nightly date."