A few notes before we start:

This is obviously an AU, with it being a crossover - timelines have also been adapted where necessary, with Lestrade, Donavan, Sherlock and John etc are all in fourth year, which is a year above Harry's third. So the story starts in The Prisoner of Azkaban. Don't expect slash, or any pairings for now - I doubt there will be any unless I bring Mary into the story at some point. There's also going to be no bashing, however you may see Sherlock humiliating some Harry Potter-verse characters with his deductions. This is a rough adaption of the 'A Study in Pink' episode from the TV series - itself an adaption from 'A Study in Scarlet', and sequels - if there are any, will follow the same pattern as this. I'm aiming to get 9 chapters for the lot - but we'll see.

Also, story plug - if you're a fan of Supernatural as well, go check out my Intervention story that I have currently ongoing in that section. I'll update a chapter of that before returning to this, and try to keep to my rough structure of one new Chapter a week for either storyline - so you'll get Intervention one week and A Study in Red the next. Depending on Days Off/Free time I will update quicker. Maybe.

CHAPTER ONE

I.

"SO, WE CAN safely say that within the last three months, we have successfully found any missing valuables, any items that you may have been missing," a fourteen year old Lestrade said one afternoon in the Great Hall. It had just gone lunch so the teachers had retired to their lessons, and but regardless, students had been gathering around him now – the would be Auror, always leading. "A missing Toad, I believe... Neville Longbottom?"

"Thank you," the young third year said, approaching Lestrade to collect his pet. They had started off a lost and found collection, as too many things went missing at Hogwarts that never showed up again, something that the Teachers weren't doing enough about, and with his fellow Gryffindor classmates, Donavan and Anderson, they'd managed to become the go-to people for solving problems lately.

However, words started filtering through in midair, no doubt conjured by a wand, appearing in front of the students' eyes, a sparkling yellow. "Wrong." They didn't have to wait long before they vanished, earning confused looks by the other students.

"It just says, wrong," said Oliver Wood, confused. "How can a thank you be wrong?"

Donavan cleared her throat. "The message was referring to the earlier statement. Has anyone here lost something that they don't see among the lost and found items?"

"Ahem," said the student, clearing his throat from the other side of the room. "I don't believe we've been introduced, my name's James Twist."

Anderson snorted, and cleared his throat promptly under a disapproving look from Lestrade. "What've you lost, James?"

"My sister," James admitted," causing a shocked gasp to filter through the room. "She disappeared yesterday, as it turns out. Nobody's seen her since. I had to go to the Gryffindor Dormitory to look for her and there's been no sign."

"Your sister, you say," Lestrade said. "Are you sure she's just keeping out of your way?"

"Well, you see, we're both muggleborns," James said, with a smile. "And our route back from class regularly takes us past the bathroom where Slytherins frequent, which means we have to take it together, or else, well.. we all know Gryffindors aren't too popular with Slytherins nowadays."

"You know, James. The idea that you've suggested is preposterous. A Slytherin wouldn't go so far as to kidnap a Gryffindor, not when the castle is under close protection because of the threat of Sirius Black."

Wrong.

"There it is again," Neville observed, glancing at the word in front of him. "wrong."

Donavan whispered to Lestrade as the words vanished once more. "You've got to stop him doing this. He's making us look like fools."

"If you can tell us how he does it, I'll stop him," agreed Lestrade, glancing at her, and then back to James, louder this time. "But a student... missing? Wouldn't Dumbledore have been alerted by now?"

"I don't know the password," replied James, somewhat embarrassed. "I tried telling the other teachers, but they wouldn't listen. Kept telling me she just wants to avoid me."

"Do you have any reason why she might want to avoid you?"

"No," James admitted. Honestly? Lestrade wasn't sure. And obviously, as it seemed – neither was Sherlock Holmes.

"We know what it says," Lestrade filled in, for he could tell that Hannah Abbot was just about to ask a question. "Now, James, the password I believe is currently Sherbet Lemon. Missing people might be a bit out of our paygrade, but the Headmaster knows everything about what goes on in this castle – he'll find her. Just do us a favour, and don't tell Sirius Black, well you?"

There was a loud round of laughter at this – the very idea that Black might be in the castle seemed impossible.

James waved his hands up as a gesture of thanks in Lestrade's direction, and filed out of the Great Hall with the others, who were collecting their missing items. Donavan started counting the Sickles that she'd collected, and smiled. "We don't have to pay the freak, do we?"

"Well, he did help us find every single object," Lestrade admitted. "And, he did say that he'd found them before we started asking questions. We could have got them a lot sooner if you two had just agreed to work with him."

"He's a freak, Lestrade," Donavan threw her arms up in the air as they made their way out of the room as well. "Screw it, I'm keeping the money. If he wanted it so badly he'd be here by now."

II.

WHACK. WHACK. WHACK.

"Bad morning in lessons, was it?" Molly asked, glancing at Sherlock, wincing as he whacked the corpse of the House Elf with a stick. They were in a room just off from the kitchens, and this was – a Dumbledore approved, way of getting results – the Headmaster had been kind enough to grant Sherlock what he wanted, and whilst it had been unorthodox, he'd worked out how brilliant Sherlock's mind was – and knew that anything that could maximise the potential that was already there should be allowed free reign, provided he didn't go too overboard.

Plus, Dumbledore didn't want the Ministry finding out that somebody was murdering House Elves. Sherlock also kept the problem secret from the rest of the school – it was better for privacy that way, and had a lot more free time than the likes of Snape and Lupin, the latter of whom would be investigating but was not – Sherlock had worked out that he was a Werewolf from the moment that he saw him – and it was coming up to his time of the month, with meant that the Professor was frequently feeling more ill by the day.

And Snape was too busy with other matters, believing that the deaths of House Elves was beneath him.

WHACK. WHACK. WHACK.

Once the stick was removed, Sherlock turned his attention to Molly. "I need to know what bruises form within the next hour. A Slytherin's alibi depends on it – message me once I'm out of lesson."

"I was thinking, Sherlock," Molly said, nervously, stopping and causing the boy to turn around.

"Oh, that's very good, Molly. Thinking is important."

Molly rolled her eyes, clearing her throat and blushing. "I was thinking, would you like to have tea, Maybe..." In Hogsmede? With me?"

She never finished her sentence. "That's an excellent idea," Sherlock said, with a smile. "Milk, Two sugars. You can have it ready for me when I leave. I fear I may have stumbled onto a much more pressing case than the murders of House Elves, however Molly... this may be quite interesting to find out what the results give us. Don't forget, will you?"

III

"JOHN, JOHN WATSON?" Limping towards the Potions classroom, the young Gryffindor Fourth year turned and looked at the Hufflepuff who had just called his name.

"Mike?" John asked, raising an eyebrow at the overweight student who had just hustled past him. "What're you doing here? I thought you had Defence with the Hufflepuffs."

"Yeah, well, we can't all have what we want, can we?" Mike said, with a shrug. "Teacher called in sick for the day, and they weren't able to find a cover in time. So we got the lesson off."

"And you made it down here in," John checked his watch – it was one of the few muggle technologies that worked at the Castle, and he was grateful for it – a timekeeper that didn't do anything fancy, and whilst other wizards dismissed it for its normalcy, John didn't. "What, ten minutes? Something up?"

Mike was visibly out of breath, and John winced in sympathy for his friend as a group of laughing Slytherins walked past. Pulling John aside into a corridor that led him away from the Potions classroom, Mike said, "Listen, I've been told to warn you. Tomorrow, fourth years are being paired with students from other houses for a year long assignment. Something about inter-house union."

"Seriously?" John asked, wincing slightly, and frowning at what his reputation meant. For the past two years, he'd been a star beater in the Gryffindor Quidditch team, the same team as Harry Potter – consistently keeping out one of the Weasley twins – whoever had gotten into trouble on the day of the match. Such an act had not only earned him ire from the non Gryffindors for preventing their best Chasers from scoring, but also from the Gryffindors who were pro-Weasleys – and given the nature of that house, there was a lot of them. It was only because of Oliver Wood that he had stayed on the team, with Oliver putting Quidditch talents above friendships and family. It had only been last year, following the year with the Chamber of Secrets debacle – that John had gotten his leg injured in an attack from Death Eater sympathisers.

It was enough to injure it on a permanent basis and put him out of the Quidditch team for the foreseeable future, much to his chagrin, but at least he was back on the Gryffindor's good books. Not the Slytherins, however. "Seriously," Mike replied. "Officially, Snape is going to pair you with a student in the next class."

"Yeah, because there's an idea that's going to work," John remarked. "Wouldn't it have made more sense to make the students from the Houses with the bitterest rivalries not be paired together? That's just asking for trouble."

"Well, take it up with Dumbledore, not me. Don't shoot the messenger," Mike said, chortling. "Anyway, you have fun. I've been paired with someone called John Finch – I look forward to meeting him, I must say. Anyway, you've got Potions. So I'd best leave you to it – can't have Gryffindor losing anymore points now, can we?"

"No, Mike, we can't," said John, all too well remembering the incident with Anderson, Lestrade and Donavan in second year, where they'd tried to go after the Chamber of Secrets themselves as some part of 'vigilante' group. They never managed to find the location however, and upon being caught whilst out of bounds, they'd been in detention for the rest of the year, and it was only because of the actions of Harry Potter that they'd won the cup. After all, how was Dumbledore going to deny a twelve year old who had just slain Slytherin's monster?

Wincing as he moved his walking stick forward, John made his way through the crowd of students, bidding Mike a farewell as he headed to the classroom. He could already see students milling about outside. Once the doors were opened, he walked in – and found himself sat next to a Slytherin, with black hair, wearing a scarf. Giving the boy a strange look, John turned his attention to the Professor, who was – if Mark was to be believed, about to make an announcement.

"Ahem," Snape coughed, clearing his throat. "I have been instructed by Headmaster Dumbledore to inform you of a recent change in the school's curriculum that he believes will be beneficial for encouraging Inter House relationships."

There were a few murmurs around the classroom at this, but they were quickly silenced by a stern look from the Professor. "Now, this is unfortunately one of the Headmaster's schemes that I cannot avoid without facing the consequences, so as a result this lesson will be spent with you working together with your newfound friends. And before you get any ideas, I will be choosing who works with whom."

John looked across the room, suddenly feeling uncomfortable next to the Slytherin whose name... was it Helmes? Holms? Something like that, he wasn't too good with names, and he only vaguely remembered him being called at the Sorting Hat. He'd only been sat next to him because that was the only seat free – normally he would have sat with his friends, but they'd already paired up.

So he was on his own. With the Slytherin. "Anderson," the first Gryffindor was called out. 'Starting in Alphabetical order, then,' John observed, realising that he would have to wait a while. Gryffindors first. Anderson looked up at being called. "Reese."

Anderson looked over at the bulky fourth year in the corner of the room, sharing a glance with Donavan. "Carter," Snape moved to Cs. "Winchester." And then, "Donavan" was paired with "Thrace", "Fusco" with "Adama", and John started to lose interest. It would be a while before he reached the Ws. Zoning out for a minute, John found that the wait for the Ws came quicker than anticipated, and he was brought back to attention by Snape's voice calling his name. "Watson, Holmes."

Holmes. John knew he'd been close, and he couldn't believe his luck, really – he wouldn't have to move, like many of the other students were doing. It wasn't Helmes or Holms, it was Holmes. The name of an older brother rang a bell, a Ravenclaw? Mycroft? Something posh, that could only come from a wizarding family. Nobody in the muggle world would name their child Mycroft, unless they were incredibly mean. "Um," John mumbled, addressing the boy. "John. John Watson."

"Afghanistan or Iraq?" Holmes asked, addressing him.

"I'm sorry?" John asked, confused.

"Afghanistan or Iraq, learn to listen. Which war did your father fight in?"

"How do you know about my father?"

"The watch," Holmes said, pointing at it. "It's clearly muggle, and quite old. Now, from previous experience, most muggleborn teenagers these days don't use watches, even when not at Hogwarts. They use mobile phones, very quick – I must say. I would ask Mother to get me one of these but given her anti-muggle nature, that wouldn't go down well. So the only logical conclusion must be sentimentality. The watch, whilst old – is – was, quite expensive in its time, and no self-respecting teenager would spend this much money on it. Now, was this from the mother, or the father?"

"F-"

"-ather, obviously," Holmes drawled. "the scratches. Unkempt. Traces of alcohol, I'm sorry, your father was a drinker. Quite frequently, I'm afraid – and often clumsy. Or clumsy enough to have his watch dropped in his drink, at the very least. But before that, your father was a war veteran, I can tell that from the scratches on the back of the watch. He took it with him, abroad. It doesn't take a genius to tell that they are where the bullet has grazed the edge."

John blinked, taking off his watch and looking at his interior. Before his newfound companion could be proved right, however, Holmes spoke again. "So, Afghanistan or Iraq?"

"Afghanistan," John said, awed. "Wow. That was... that was amazing."

"Was it?" Holmes asked, raising an eyebrow at him.

"Not the reaction you normally get?"

"No," admitted Holmes.

"What is?"

"Piss off."