"Oh, Sherlock, moping again?" Mrs. Hudson asked as she popped in, her cheery demeanor darkening Sherlock's already melancholy mood. He paused in his violin playing to regard the woman with an almost icy stare.

"I do not mope Mrs. Hudson. Nor do I sulk, before you make that equally ridiculous accusation." He droned in his deep baritone. His sharp ears could hear someone, most likely a female, talking downstairs. A phone conversation, it sounded like. Or an individual who heard voices in their head.

"Tea, dear?" Mrs. Hudson asked as she helped herself to Sherlock's kitchen.

"Yes, fine." Sherlock consented, sensing the older lady had further business, but knowing she'd get there in her own time.

"Sherlock, are you interested in meeting a potential neighbor?" She asked, setting the kettle on.

"Dull." He spat as he set his violin in the case and went to sit in his chair, his dressing gown billowing out behind him as he moved.

"She's really a lovely girl." Mrs. Hudson tried to coerce, "And I know you've been so lonely since John left."

"I'm not lonely, why would you think I'm-"

Mrs. Hudson held up a stack of photographs from his kitchen table. Photos of John, Mary, and their daughter, Kyla.

"I was making something." Sherlock defended. "Since John and Mary are too busy most days to make one, I was putting together a photo album." He refused to look at the older woman, as she was beaming at her tenant in a heartfelt manner.

"That's very sweet of you, Sherlock. Well, I think she'll be taking the basement then. Unless you would like to try her out as a flat mate."

"Not interested." He huffed, his ears perking up as someone, most likely the girl, started coming up the stairs to his flat, pausing half way up.

"Mrs. Hudson?" Female, American.

"Up here, dear. I've put tea on." His landlady's response made Sherlock scowl.

The young woman made her way up the rest of the stairs and took a few tentative steps into Sherlock's flat. She couldn't have been more than twenty-two. Thin and a little shorter than average. She stood straight, her shoulders tense. Nervous. She gave him a small, lopsided smile.

She was of a milky caramel complexion, with dark eyes and inky black hair that cascaded down her back. She wore black thick-rimmed glasses and was dressed in a midnight blue blouse and dark jeans that were almost skin tight. On her feet were a pair of black silver studded flats. She had a dove grey messenger bag made of durable cloth slung across her chest.

Sherlock watched as her eyes took in as much of his flat as they could. Sherlock doubted she observed half as much about him as he did about her.

"Hello, I'm Erin." She volunteered her name, the few seconds since her halfhearted smile having passed in silence.

"Sherlock Holmes." He said nothing more to her. Seeing as his deductions had already been made, he resumed paying her no mind.

"Nice place. Have you lived here long?" She asked, venturing a few more steps in.

"Does that matter?" He snapped.

Erin's lips turned down for a fraction of a second before she gave Sherlock an awkward smile. "I suppose it doesn't."

"Sherlock, don't be rude." Mrs. Hudson gently reprimanded. As she brought a tea tray in and set it down on the coffee table.

"No, it's alright. No damage." Erin soothed, her calm demeanor making Sherlock narrow his eyes.

"Here you are dear." Mrs. Hudson held out a cup of tea for the girl. Erin took the few steps to take the offered cup with Sherlock's eyes upon her.

"Oh." He breathed the word so it was drawn out, his observations falling together.

Mrs. Hudson gave him a sharp look. "Don't start Sherlock." She warned.

Erin looked between the two, a polite but questioning smile on her face. "Sorry, am I missing something?"

Sherlock opened his mouth to speak but Mrs. Hudson quickly cut him off. "He has a unique talent. He can deduce everything about you. Most people get offended when he does though."

Sherlock huffed.

"Let's hear it then." Erin prompted, her face showing her curiosity.

"American, foster child until your mid-teens, when you ran away. You've worked hard to get here and have been in London two days and are in a hurry to find somewhere to live. Two-two-one was not your first choice, but here you are. So, you've upped your price range and you can't just be a student to afford it. You have a large amount of money saved, possibly a trust fund. You also have trust issues with your boyfriend." Sherlock's lips twitched up momentarily at the young woman's stunned expression.

It took a moment for her to recover, "How did you know that?"

"The way you speak tells me American. No indications of any other nationalities. The way you pronounce certain syllables leads me to believe Oklahoma."

He quickly jabbed his finger towards her bag "The insignia on your bag clearly says Oklahoma as well, so there's my confirmation there. You paused and hesitated to enter my flat and have been hard pressed to move anywhere near me, but you have no problem approaching Mrs. Hudson. You have a subconscious fear of men. One must wonder why. Early childhood trauma most likely, probably at the hands of your father."

He was staring intently at her face, his eyes unsettling her as she forced herself not to look away. "By the fact that your left leg is a prosthetic and too short, I'd say you've had it awhile. When did you stop growing? At age fifteen, sixteen? You haven't paid attention to that leg for a while, so you had that prosthetic put on a few years prior to the end of your growth spurt. Why have you gone so long without replacing it? Negligence is an option, but no, that's not it. You would have had care takers, in theory."

He paused to take a breath, "A missing limb and fear of males leads me to believing those care takers were not your parents. So, foster care. You ran away, and since still to this day you've yet to replace the limb, you were never caught and it faded to the very back of your mind. Clearly clever and you wouldn't be standing here if you hadn't worked hard. Taking your studies abroad isn't cheap. You had to work for this opportunity."

He pointed towards her eyes and then her bag again. "You have clear signs of exhaustion in your eyes and your passport is clearly visible in the mesh compartment of your bag, you haven't adjusted your watch yet. But you obviously aren't fresh off the plane either as you have no luggage in tow. So, jetlagged and staying in a hotel. Seeing as the new school year starts soon, I'd imagine you'd want to be settled quickly. Why else would you go out exhausted to look at flats? You have ads stored with your passport, some circled and marked out. Shall I go on?" He fixed her with a bored expression.

"No, I… I get it." Erin took a deep breath, "That's amazing. Eerie, but amazing."

"Did I get anything wrong?" Sherlock asked, swelling with pride, confident what he had spouted off was not wrong.

"I don't have a boyfriend," Sherlock opened his mouth to protest, "I have a girlfriend. Well, fiancé, these days."

Sherlock sighed. "Always something." He narrowed his eyes at her. "No ring."

Erin pulled a chain out from under her shirt. "We got them secondhand, luckily hers fit. It's not your fault, these are things anyone could miss."

Sherlock let out a huff, "Perhaps you won't be such an insufferable neighbor after all." He allowed, suddenly perking up as his phone chimed.

"I'll sign her then, shall I?" Mrs. Hudson asked, as Sherlock regarded his phone with hopeful eyes.

He nodded his consent as he stood from his chair swiftly, a smile spread across his face. "Lestrade has a case. I should phone John, I may need him. Must run." He made excuses as he abandoned his dressing gown for his Belstaff. Things were looking up at 221B.

Erin lived at 221 Baker Street for three months when the night rolled around that would change Baker Street forever.

It started with a call, as usual. Erin had been bringing in a bit of shopping as Sherlock and Doctor Watson came barreling down the stairs.

"Off and out, boys?" She asked, stepping out of the way.

"Yes. Triple homicide. The only clues left behind are a cactus and a tube sock, according to Lestrade." Sherlock started, looking pleased as punch.

"Sounds right up your alley." Erin chuckled.

Sherlock gave her a lopsided smile as he wound his scarf around his neck. "Well, I shouldn't bother you much tonight."

"Be safe!" She called after them. Doctor Watson turned and waved before he ducked into the cab behind the consulting detective.

Erin dropped her shopping off in her kitchen, abandoning it for her work, which was stored in the only bedroom of 221C. As she settled in, she briefly thought of the man she worked for. He expected results from her research. And soon.

Erin pulled out her notes and loaded her last test results onto her tablet. She was almost ready to start chemical trials on humans. She was so close to getting the results he wanted. It was just a matter of getting the chemicals active time to a manageable state. She was just reaching for her safety goggles when her mobile began ringing. Her employer. Important business, no doubt.

"Sir. Erin speaking. The chem-"

"There is no time for that right now, I'm afraid. You're about to have a very unwelcome visitor. Arm yourself. I'm sending back up to your location." His calm voice set her on edge.

"I understand." She responded, immediately going to her desk and opening the top drawer to retrieve her hand gun.

"Protect yourself and your research at all costs." With that, the call was ended and only a second later, the door to her flat was kicked in.

"Oh, my lovely little chem~ist." A male voice sing-songed. "Do come out and play." Irish accent.

Erin swallowed as she flicked the safety off before raising the gun and walking out of her work space.

The man was someone she recognized. Her employer had been thorough in telling her how dangerous this man was.

He raised his eyebrows as a half-smile quirked up his lips. His eyes, subtly alight, were inky dark like his hair. His suit was a lighter toned grey.

"Now, it that any way to greet a house guest, Ms. Stevens?"

She didn't flinch at the fact he knew her name. Her real name, not the alias she had been assigned. "To what do I owe the pleasure, Mr. Moriarty?" Erin asked, keeping the gun aimed at him.

"I think we both know why I'm here. The chemical that you've been ordered to work the kinks out of. I want it. And I'm willing to pay. Handsomely… Or, given your apparent reluctance, I could just kill you."

She fought the urge to smile. "We're in a basement level flat. You're snipers won't work here."

"Oh. You know that old trick, do you? My, my. Holmes certainly is thorough isn't he? Tell me, does Sherlock know?"

When Erin remained silent, Jim shrugged, his eyebrows raised. "Not one for conversation?" He asked, feigning disappointment.

"Not when I feel my life or work is being threatened, no!" She scoffed, despite herself.

He gestured over her shoulder with two fingers. "Is that were you keep it? I'd very much like to take a peek."

"Drop dead." Erin growled, trigger finger giving an involuntary twitch.

Moriarty looked amused as he shook his head. "If you don't watch your tone, that's exactly WHAT YOU'LL DO!"

Erin tensed, being shouted at put her on edge quicker than anything else. Years of abuse had a funny way of doing that to people.

Moriarty took a moment to reign his temper in. "It may not be today, it may not be tomorrow. But if I don't have your full cooperation, I'll find you. No matter where you try and hide. And I'll slit you from gut to gullet and watch your innards pool on the floor."

Erin couldn't stop the laugh that sounded half forced from escaping her. She noticed this caused a vein in the side of Moriarty's neck to start jumping. She had made him angry.

"What's sooo funny?"

"You wouldn't be the first to try."

The smile he gave her clashed with the cruel look in his eyes. "Go around making a lot of enemies then?"

"Not on purpose, let me assure you."

"I find that hard to believe. Now, with the civilities out of the way, let's go take a look at your work. I find myself more than a little curious about this "Wonder Drug"."

Erin scoffed at the idea of his threat being anywhere in the range of "civil", but she lowered her gun as he walked towards her. She tensed as he leaned in to whisper in her ear. "Everyone has their price. Just name yours."

She jerked her ear away, gripping the gun tighter. He chuckled, amused, before continuing towards her work space. She resignedly followed him into her lab, hoping her back up wasn't going to take much longer. She did love her job, she just didn't want to die for it.

Moriarty was slowly circling the equipment, peering at the subtle changes of the serum as it went through the concentrating process. Many moons had seen Erin take its color from a deep, muddy amber to a subtle rose water pink.

"How close is it to being done?" Moriarty asked, picking up a sample of the highest strength she had yet produced. He shook the delicate vial gently a he stared into the light through it.

"Until testing and results are completed, I don't know. The effects haven't yet been test. I've been pushing for clearance to start testing for-"

"Get Your Hands Up Now!" An armored man shouted as he rushed into the room closely followed by three others. All wore similar armor and carried high caliber rifles, all aimed at Moriarty.

Erin jumped when they charged into the room, her hand going to her chest. Moriarty only smiled a shit-eating grin as he raised his arms, vial still clenched in his hand.

"Ms. Stevens, are you alright?" A man with chestnut hair and hard eyes, who stood with impeccable posture, waited just outside the doorway to her makeshift laboratory.

"Yes, sir. I'm fine."

A dark chuckle made her eyes flash to Moriarty.

"Too little, too late." And with those words, he crushed the vial. The glass shattered and the serum entered his blood stream. Erin stood with her mouth agape. Moriarty flinched, his eyes screwing shut, no doubt at the burning sensation now coursing through his veins. When his eyes opened, he seemed dumbfounded to have four guns aimed right at him and blood no doubt staining his expensive Westwood suit.

"Um… Excuse me, I seem to be bleeding. Can someone he-"

"What the bloody hell is going on here?" Erin's heart dropped. Sherlock was home.

Mycroft, being the only one outside the room, had a clear view of the door to 221C. There stood Sherlock, John, and Gregory, who was giving him an apologetic and sheepish look.

Mycroft rolled his eyes, exasperated. 'Imbecile!' he snarled in his head, fixing Gregory with a look.

"Hello, brother mine."

-End Chapter One-

So, welcome to my new story. I have never written a Sherlock fiction before, so bear with me. I'm writing this for a friend who claimed there were no decent Sheriarty stories (I'm sure she was just looking in the wrong places), so she asked me to write and now, look what I've done. By all means, let me know what you think, if you wish. This is a slow(ish) burn. I've not had anyone proof-read, so all mistakes are mine (I'm also not British).