The violin.

A beautiful instrument, and one that Sherlock Holmes' hands knew far too well. It helped to think, and in this case, he was thinking about the rather ridiculous prospect of love. Specifically, being in love with Irene Adler. He supposed it made sense that anybody who found out about the fact he'd saved her life would think that – but Sherlock was not one to fall victim to that dangerous disadvantage, just like The Woman had.

He supposed that she was lucky his phone had made that rather inappropriate sound when she text him her goodbye. It let her know she wasn't going to die.

Of course, John wouldn't have known about any of that, but that meant Sherlock knew about his flatmate's blatant lie about Irene going into witness protection. He didn't blame John for lying, he was trying not to hurt his feelings. Whatever those were.

He paused for a moment, electing to scribble down the notes of the melody he was composing before finally setting down his violin. He stared out the window, wondering what could be going on in London in the month of January. Were people still celebrating the new year? He wouldn't be surprised if they were, Londoners looked for any excuse to drink despite the prices being ridiculously high for a pint.

It seemed as if his curiosity was high enough to warrant him leaving the flat and going for a walk.

He grabbed his coat and scarf, pulling them on and debating whether or not to call up to John and tell him that he was heading out. Then again, there was a good chance John wasn't even in the flat, and Sherlock wouldn't have noticed if he'd come back anyway.

Once outside 221B, Sherlock walked to the south end of Baker Street and continued walking until he came towards Oxford Street. He checked his watch: it was some time past eleven at night, meaning that the busiest street of London was fairly empty apart from the midweek drinkers and late night workers making their towards tube stations and train stations in an effort to get home.

How wonderfully boring it must be to have a regular job that made you work overtime. There was no way on Earth that Sherlock could do that. The same thing over and over? Ha! As if.

Something caught his attention as he wandered past an alleyway. Noises. Not good noises. He sighed, wondering who could have possibly thought it was a good idea to walk down a darkened alley lit by only one dim street light at this time of night. Man or woman, they were an idiot.

Regardless, it gave him something to do.

He turned left and crept down there, and watched the curious sight before him.

There was a woman in trouble – perhaps a few years younger than he was – but she was holding up her own rather well. Her attacker was about the same height as her, and he had a knife against her throat, holding her in an arm lock too.

"I can feel how blunt that knife is..." the woman told him carefully. "The most damage you'll do is put me in A&E, not kill me – I mean, you've fucked my wrist up enough already... You want the bag that badly? Fine."

She tossed her bag slightly to the right of her, and the minute the man made a move for it, she elbowed him in the stomach so that he doubled over. That was when Sherlock decided to hop in and help.

There was an open skip with a broken shovel in it, and he grabbed that and gave the man a good whack over the head with the spade side of it. He fell to the ground, half conscious, so the woman kicked him in the face and he was out like a light.

In the moment that the woman gathered up her things, Sherlock took the time to survey her.

Long, curly brown hair tied up in a ponytail, tired blue eyes and relatively smart outfit that suggested she worked in an office, but not in one that she liked.

"Cheers for that," she said to Sherlock, and he grunted in response, turning away. The woman scurried after him. "Oi! Not gonna give me an explanation? And shouldn't we call the police?"

"Why should I? I was bored, and you're an idiot. And the police won't do anything, that man is homeless." Sherlock stopped on the main street again, waiting for the woman to catch up with him. "Then again, you don't look like an idiot and you certainly don't act like one. My guess would be that you use that alleyway regularly as a shortcut home."

A half smile appeared on her face as she caught up to him and they carried on walking together. "Huh. Got it in one. Not many people can do that, except..." Now it was her turn to survey him, and Sherlock spotted the recognition in her eyes. "Well, I would say it's a pleasure to make your acquaintance, Mr Holmes, but you wouldn't give me the same courtesy."

"Hmmm. Definitely not an idiot."

She rolled her eyes. "Yeah, I got that. Now. Where we going? My flat's the other direction."

"You said something about your wrist, my flatmate's a doctor. You can put two and two together, yes?"

"I should hope so, considering I work with computers."

Sarcasm. The lowest form of wit. In this case, Sherlock could forgive it, because this woman hadn't tried to punch him yet.

"Katrina Jenkins, by the way," she then said. Sherlock made a huffed noise in response. "Wow, you are quite the arsehole…"

"There it is. Took you longer than other people, but we got there..." he almost seemed amused by that. "You're not from around here, are you?"

"Nope. Would you like to guess where from?"

"I'd say Sheffield."

"Close, but..."

"Chesterfield?"

"Yes. How'd you figure that one out?"

"Your voice holds a hint of an accent on particular words. Not noticeable enough for people to outright think you're not from the South, but noticeable enough to consider the Chameleon Effect."

"Parents decided to move south when I was about eight," Katrina said, as they approached Baker Street.

"I really don't care about the details, Miss Jenkins."

She grimaced. "My boss calls me 'Miss Jenkins,' so Katrina is just fine with me."

Sherlock shrugged as they stepped up to 221B, and unlocked the door. "Formalities. It's um… it's polite, isn't it?"

"Something like that. Not that I care for politeness half the time," she said, following him inside and up the stairs.

"Are you sure about that? You were oddly polite to me."

"You helped me sort of beat up a guy who was attempting to mug me with a blunt knife. I had to be polite," Katrina replied in a matter of fact voice.

Sherlock smirked as he tossed his coat onto the sofa. "John!" he then called out. "We have a client. Sort of..." He turned to Katrina. "Sit there." He pointed at the wooden chair by the desk. Katrina gave him an odd look, but went there anyway.

A few moments later, a jumper clad man came trudging into the room. He looked like he had just been about to go to bed.

"What?" he sighed at Sherlock, who gestured with his head towards Katrina. "Really?"

"I'm assuming she has a sprained wrist, but I'd rather have your… professional opinion."

"So she's not a client?"

"No." Sherlock grabbed his laptop and settled in the blue armchair, pretending to ignore his flatmate and Katrina, but he kept shooting glances at them every now and then while the good doctor fixed up the woman's wrist.

The room was silent, but from every glance Sherlock took at Katrina, he began to learn more and more about her. It took about ten minutes before he cracked and decided to grill her.

"Necklace. Where did you get it from?" he asked her.

"Excuse me?" she jumped, while on her way out.

"Necklace. Tiny diamond, but still too expensive for you to buy on the current wage you earn, although your quite charming two bedroom flat in Brixton says otherwise..."

She didn't even want to know how he knew about that.

"Not that it's actually any of your business, but the flat in Brixton is cheaper than you think, and necklace was a gift from someone I dated a couple of years ago." Katrina turned back to John. "Thank you, Dr Watson."

He smiled. "No trouble at all. Um… see you around?"

"Maybe." Katrina glanced at Sherlock. "Good night, Mr Holmes. I think I owe you a favour now."

And with that, she left.

"Take a night bus, would you?!" Sherlock called after her, but she was gone. He scowled at the empty doorway, while John looked at him oddly.

"How did you find her?" he then asked his friend.

"I went for a walk, someone had a knife to her throat." Sherlock shrugged. "She would have done fine on her own, if I'm honest, but I needed something to do."

"You'll get a case soon, Sherlock..." John said, getting up. "But for Christ's sake, let me sleep."

John left the living room and retreated to his bedroom, leaving Sherlock to mull the woman's last words to him over in his mind.

I think I owe you a favour now.

He groaned, realising that he would most likely run into the damn woman again.

Well, at least his life would be a little more interesting on his off days, now.