Hi everybody! This is only a preview for now, I'm still in the process of writing this but I wanted to get a feel for how people would respond to it, so I decided to post the first chapter of my future Sherlock/OC story. Can't guarantee when more will be posted, but constructive criticism is welcome and appreciated! Let me know how this first chapter works for you, I'll update it if needed before I post the next chapter.

I do not own anything you recognize, only Katelyn. Enjoy!

"We had a break in just the other day, and an explosion across the street right before that. Oh, but, don't worry dear. The boys have said they've got that all sorted out. You'll have nothing to worry about."

The young woman nodded, not entirely reassured, but trusting her new landlady. She headed towards the door to the basement flat, small box in hand. She'd only been in London a few weeks, and hadn't had time to purchase anything but the necessities. She had only what she'd taken with her from the States, items from her past she was too sentimental to let go of.

"Well, even if someone were to try to break in again, I'm sure I could handle them," she said. Mrs. Hudson let out a laugh, as the girl was quite small, and despite having some muscle, didn't look to be capable of hurting anyone. The girl only smiled and shook her head, blonde hair swishing behind her. She placed the box in the middle of the room, next to three other slightly bigger boxes, before turning back to her landlady. "Thank you again for everything, Mrs. Hudson."

"Oh, it's no problem, dear. It's good to know my old furniture is getting some use rather than collecting dust." They turned as thundering was heard coming from the stairs. The girl peeked out of her door to the main landing, only to see the end of a long coat trailing out the front door. She stared on in confusion as another person came down from upstairs. She turned to finally get a look at one of her neighbors. He was short for a man, though still taller than her, with short blond hair. His expression was one of frustration as he pulled on his own jacket, though that quickly melted into surprise when he looked up. He slowed down a bit, stopping in front of her.

"You must be the new neighbor Mrs. Hudson mentioned. Dr. John Watson," He stated, thrusting his hand out for a shake.

"Oh, hi. I'm Katelyn…Summers, but you can just call me 'Kate'. It's great to meet you."

"Likewise. Listen, I've got to dash, but perhaps you can come up for tea sometime? That way you can meet Sherlock and we can all get to know each other?"

"I'd like that. Just come and find me when you're not busy. I'll be...here," she laughed. He chuckled a bit as well.

"John!" Both blonds jumped at the shout, coming from Katelyn's other neighbor. John rolled his eyes slightly.

"I'm coming! Sorry, Katelyn, gotta run. I'll come get you when we've solved this case. Bye!" He yelled, dashing out the door. Katelyn smiled, turning to her flat so she could unpack. Mrs. Hudson had returned to her home, and Katelyn was left completely alone with her thoughts. This was something she was still getting used to. In her 30 years of life, rarely had she ever been completely alone. Only once that she could really remember, and that was years ago now. She slowly began to unpack, smiling at the idea of having a place for everything. After a while, the silence became too much for her, and she began to hum a few Beatles songs to fill the quiet.

She stopped only when she heard the front door open and close, footsteps heading up the stairs. She smiled to herself, almost deciding to go up and say hi, but she dismissed the idea quickly. There was no way to know they weren't busy still, and she didn't want to intrude on that. John would get her when he was ready. She stood up, intending to walk around the flat for a bit to stretch her limbs before tackling her last box, the one labeled 'Family stuff'.

For a while she only stared at the box, afraid of the tears that would fall when she opened it. She was so sick of crying about her decision to leave, so sick of wondering if it was the right decision.

"Guess it's what I've got to live with though." She whispered, her voice like breaking glass in the silence of her new home. "Come on, Katelyn. Don't be such a girl." With that, she sat down and ripped open the box, knowing that prolonging it further would leave it sitting there forever.

There wasn't much inside. A few bottles of red and black spray paint, her brother's necklace no one knew she had, a photo of her family, and her gun. She was still surprised at how lucky she was to have been able to get it here. She put the picture on her bedroom end table, placed the necklace around her neck, and stuck her gun in her waistband, hiding it beneath her shirt. She decided she'd use the spray paint in the morning, before going off to work. For now, she was starving, and it was with this thought that she grabbed her jacket and headed out the door, off in search of a cheap takeout place.

It wasn't until a few days later that John invited her upstairs. She sat on the couch in 221B, only a little nervous at the way her other neighbor, a man named Sherlock, was staring at her. She felt like he was scrutinizing every bit of her, like he knew everything she'd ever done, or said, or thought.

"Sherlock, take a day off, please." John scolded as he served Kate her tea. She thanked him with a smile before taking a quick sip. Sherlock merely rolled his eyes.

"I'm sorry, what is he taking a break from?" Kate asked. Sherlock smirked and began to open his mouth, but John quickly cut him off.

"Uhh, so, Kate, what do you do? If you don't mind me asking." Sherlock scoffed before she could answer.

"Don't bother, John, she's obviously a waitress." He stated, disdain lacing his voice.

"Ok, implication aside, how is that obvious exactly?" John gave a soft groan as Sherlock smirked once more.

"There's the fact that you couldn't afford your own furniture. You've been in the country for just under a month, low paying job then. Cheap clothing, also an indication of a low salary. Coupled with the slight Italian food smell since you walked in the door, waitress becomes rather obvious." Kate eyed him warily for a moment.

"Ok...what else is 'obvious' about me?"

"You have at least one brother, and your mother has been deceased for a while. You're spiritual, but not religious, and you have a history of high-risk situations."

"Ok, and how do you figure all that?"

"Your jewelry. The bracelet is older than the necklace, and there are slight indentations in the skin indicating you wear it often. It's quite a few years older than you, therefore your mothers, but you've worn it for a long time. Possible your mother gave it to you when you were young, dead is more likely. Sentiment. The charms on the bracelet are from all different types of religions and theologies, showing that you're at least slightly spiritual, but not dedicated to one theology. The necklace is a more masculine design, and as it's significantly newer than the bracelet, and not worn as often, it's a brother's, not a father's. How do I know you don't wear it as often? You grab at it every time it moves, proving you're unused to it being there. Now, you're tensed, and positioned to make a quick getaway should you need to. You also don't have a weapon on your person at this time, though I'm sure you have one somewhere, so you're either comfortable with present company or in your own hand-to-hand combat skills to be able to take care of yourself if necessary."

Katelyn sat there, intrigued and nervous at the same time. It took only a moment for her to recover.

"Holy Cristo, that was cool." She said. "Pretty spot on, actually. I have two brothers, my mom's been dead since I was a baby, and we all tended to get ourselves into trouble pretty easily. I'm not spiritual though, these charms aren't mine."

"Semantics." Sherlock muttered, rolling his eyes. Katelyn just smiled at him.

"I can tell we're going to be great friends, Sherlock Holmes." This almost made the detective jump, as he glared right at her, looking appalled at the notion. Her and John both bust out laughing at his expression. "Yep, definitely great friends."

"So, you don't mind that he did that?" John asked.

"Oh no, I don't mind. Even if I did, I kind of asked for it. I think it's amazing that he can do that. I wish I was that good."

"Oh great, now his ego will fill up the entire flat." John joked. Kate laughed.

"So, I hear you two solve crimes?" This launched a conversation that lasted for well over an hour, after the tea had all gone cold. John and Sherlock told her all about the different cases they had solved, including the recent one with a man named Moriarty.

"You almost got blown up. Sounds fun?" She tried to joke, to ease some of the tension from John's shoulders. He gave a tight smile, before telling her about his blog as well.

"You can read it if you'd like. Do you have a computer?"

"Not yet. I don't have the money for one right now, but hopefully by Christmas. I hate being without a computer, but I suppose I never actually had one of my own. I always stole my brother's laptop."

"He didn't have a password on it?"

"Not a good one, at least. It was pretty easy to figure out."

"Well I'll let you borrow mine if you ever want to read the blog. Normally I wouldn't advertise like this, but if we are going to be friends it might be beneficial for you to really understand how we work."

"John if you want me to read your blog you just have to say so."

"Katelyn, I want you to read my blog."

"Lead the way, Dr. Watson!" She giggled. Sherlock rolled his eyes once again, grabbing his violin and playing some odd notes on it.

John left a few days after that, deciding he needed a holiday after nearly being blown up. He and his girlfriend, Sarah, were going to New Zealand, and Kate promised to keep an eye on Sherlock while he was gone, though when she realized he didn't even know John had left, she determined he'd be fine.

During the ten days John was gone, Kate became very used to the sea of clients hoping the consulting detective upstairs would help them. When she wasn't at work she would hear the occasional, "Boring!" She felt bad for those clients, but it wasn't her business to say anything about tact. At night she'd hear more of his violin, sifting through the building into her ears. She fell asleep to his playing almost every night, and while she'd never admit it, she enjoyed falling asleep to it.

Kate was falling into her new life pretty easily. She'd get up, shower, dress, and hang around her home reading before leaving for work in time for the dinner rush. I'll have to invest in a TV soon, and possibly a radio, she mused on her way home one day. A co-worker had called in sick, leaving her to cover the lunch shift on her day off. She wanted to just go home, eat a sandwich, and nap the rest of the day. Back-to-back shifts like that really took their toll.

Her sandwich and nap were put on hold, however, when she discovered her door already unlocked upon her arrival home. She paused a moment, before quietly pulling her pistol out of her faux-leather jacket where she'd hidden it during work. She softly opened the door, gun at the ready, and walked inside. Sitting on the couch was a man in a dark suit, holding a black umbrella. His brown hair was combed away from his forehead, and he had a stern look on his face.

"Who are you, and what are you doing here?" Kate demanded, gun raised.

"I could ask you the same thing," the man answered, standing. Kate scrunched her face in confusion, lowering her gun only slightly.

"Excuse me? You come into my home, demanding who I am? Who the hell do you think you are?" The man smiled, though it was cold, and mocking.

"I'm possibly the most dangerous man you'll ever meet, Katelyn. Now I suggest you answer my question. Who are you really?" Kate's eyes widened, and her grip on the gun tightened. How did he know her name? He doesn't, Kate. Only your first name. That's not that hard to figure out if you have ears. Stay calm.

"I've met some pretty dangerous people, and I gotta tell you. Umbrellas? Not that scary. You want my name, tell me yours."

"Or what, you'll shoot me? You have a detective living above you. You'd never get away with it, it isn't worth it. Meanwhile, I could have you on a plane back to the U.S. in 5 minutes if I chose to. I suggest you cooperate, and tell me your real name."

"Why the interest?" She asked, not wavering a bit. She saw him clench his fists around his umbrella handle.

"What is your interest in Sherlock Holmes?"

"We had tea once. I'm becoming friends with his roommate, hopefully him too if he can pull the stick out of his ass long enough. Why are you interested in him, and if I could pull it back to the original problem, why the interest in me?" The man stared for a moment, a familiar feeling of being read coming over Katelyn, only this time it felt cold, like the man in front of her. As if she was being plunged in ice water, and all her secrets were pouring out of her like air bubbles.

"Katelyn Summers. That is the name you go by here." Kate nodded. "That name does not exist. If you plan to continue interaction with the residents of two-hundred twenty-one 'B' Baker Street, I need to know who you are."

"Why do you care so much abo- Oh…What's your name?" Katelyn asked in a soft tone, loosening her grip. The man gave a defeated sigh and rolled his eyes, as if giving in was the hardest thing for him. Honestly, it probably was.

"My name is Mycroft Holmes." Kate nodded, and lowered her gun completely.

"You're his big brother aren't you?" Suddenly it all became very clear to her. The cold stare, the feeling of having no barriers, it all screamed Sherlock Holmes. When she looked closely, she could even see some resemblance. "Alright. What do I get out of it?"

"You'll be allowed to stay in the country." He said matter-of-factly.

"Can I have legal identification?" She asked, hopeful. He nodded. "Alright, fine then. My name is Katelyn Winchester."

Kate was a bit shaken from having her home broken into not once, but twice now, but she'd be stupid if she wasn't glad for the second one. She was here legally now, and her ID had her real name on it, and she felt like she could finally leave her old life behind, the life that included fake IDs and names on an almost everyday basis. She didn't know how she was going to tell John or Sherlock though, guess she'd cross that bridge when she came to it.

She had just gotten back from work a few days later when John returned. She had elected to take a shower before going upstairs, hoping to say hi to everyone and hear about his trip before going to bed. She thought she heard a few thumps from upstairs, but chalked it up as Sherlock making a fuss about something or other. She got out, dressed quickly, and opened her door to find John already standing there, poised to knock.

"Oh, hey John. I was just about to come up and say hi. I heard you come in." She glanced behind him as she spoke, hearing Sherlock coming downstairs as well. What surprised her, however, was that Sherlock had blood slowly dripping out his nose. He gave her a look over John's shoulder, and she instantly knew something was very wrong.

"Well, Sherlock's being an arse, so I thought I'd come down here instead."

"Of course, come on in." She opened her door a bit wider, schooling her expression into one of friendliness. The minute John stepped onto her rather large rug, she dove into action.

"Cristo." John's eyes turned black, as she thought they would, and she quickly pushed him into the center of the rug before he could react. He made to lunge for her, but was forced back. Kate felt Sherlock standing behind her, his shock apparent even without her looking at him.

"Sherlock, hun, go shut the door." He stared at her a moment. "Now!" He nodded, quickly shutting the door before going back to stand with her, eyeing her warily. She walked to the edge of the rug, a small smirk on her face. "You can't get out, I've painted a devil's trap under the rug. Knew it'd come in handy. Now, why have you possessed John? What could you possibly gain? Obviously it's to get to me, but why? I'm not important."

The demon said nothing, only glared at her.

"I'd start talking demon. I know how to hurt you without hurting John."

"You're not the target," He snarled. "You're just leverage."

"I see. You're not very bright, are you? Tell the rest of Hell that I'm not with them anymore. It will do no good to come after me." Before the demon could reply, she pulled out her phone, searched for only a moment and pressed play. Instantly Latin filled the room, spoken in the deep voice of her twin brother.

"Exorcizamus te, omnis immundus spiritus, omnis satanica potestas, omnis incursio infernalis adversarii, omnis legio, omnis congregatio et secta diabolica..."

When the exorcism finished the demon tilted its head toward the ceiling, spewing out a cloud of black smoke. When it'd all left, John slumped forward, and Sherlock and Kate immediately ran to him.

"John? John! John, wake up!" Kate urged. John slowly opened his eyes, giving a shout of fright when he saw where he was.

"Wh-what the bloody hell was that?!"

"First things first, are you alright?"

"Yes, I'm bloody alright, what the fuck was that?!"

"I too, would like to know." Sherlock spoke from beside her. Katelyn sighed heavily, before getting up to get a wet towel for Sherlock's face.

"Let me clean you up. I'll explain everything, I promise." He eyed her warily before nodding once, and she pressed the cloth to his lip. "First, just let me say that I am so incredibly sorry this happened to you, John. I assure you, it'll never happen again, to either of you. I'll make sure of that." She gave the cloth to Sherlock so he could clean his own face, as he was being a bit fussy about it. She walked to her bedroom for a moment, coming back with two odd necklaces. "Here, wear these. As long as you have them on you won't be possessed, though I do suggest getting anti-possession tattoos if you decide to continue associating with me after this." John put his on eagerly, shaking as he did so. Sherlock was more skeptical, however, and stared back and forth between the necklace and the girl standing before him. Seeing she wasn't going to speak until he put it on, he did so, though rather begrudgingly. Katelyn heaved a great sigh.

"My name is Katelyn Winchester. My brothers are Dean and Sam Winchester. I was born in Lawrence, Kansas to John and Mary Winchester. My mother was killed by a demon when I was six months old. This led to my dad becoming what's known as a Hunter, and we all followed in his footsteps. That's what my family has done my entire life. Hunt ghosts, demons, shape shifters, anything supernatural. You'd be surprised at the things that have happened to us, the things we didn't even know were actually real. My dad died a few years back, it was just Sam, Dean, and I from then on, and I left them behind when I came here. I wanted out. I am out. I don't hunt anymore, but it doesn't mean I'm not prepared. Now, I understand if you don't want to talk to me ever again, it's fine."

"Demons don't exist." Kate let out a single laugh.

"Well, Sherlock, they do. My mother was killed by one, my dad was killed by one, John was just possessed by one. What more proof do you want?" Sherlock sat there, staring straight ahead for a moment.

"Alright, demons are real. Nothing else is. Though it might be useful to have you around."

"What? How?"

"Always good to have another pair of eyes on a case, a third opinion. Especially if that person has solved cases of their own, however misguided and ridiculous their findings obviously were." Katelyn only rolled her eyes at him. If he wanted to deny the existence of everything else, she was not going to stop him.

"Alright then...John?"

"Well, I certainly don't want anything else coming after one of us. Whether they're real or not, I'm not sure yet. I'm not sure what I think, I only know what's just happened to me, and I'd rather not have it happen again. You're still my friend, Kate. Even if you are completely nuts." Kate let out a small laugh, which quickly turned into relieved, tired giggles. Sherlock and John slowly joined in.

If there were any doubts to them being friends before then, they were quickly dashed. For better or worse, they were stuck together now, and this was only the beginning.

So there it is. Katelyn is an OC of mine (obviously), and this is a bit of a crossover with Supernatural. I'm gonna try to keep any spoilers for that out of here, except what's important to know for this story. As far as where in Supernatural's story we'd be, just caught up to date with whatever. Even new episodes, imagine they've happened to Kate too, because you never know what they're going to do with that show. So unless I say otherwise, the entire plot of Supernatural, past, present, and future, has all happened to Kate, ok? As far as Sherlock's storyline, this chapter is set between The Great Game and A Scandal in Belgravia, and will continue into season 3. I'll try to have more soon, but nothing's guaranteed. Thanks for reading guys :)