221B Baker Street was always messy. John had grown to accept that. Whether it was eyeballs in the microwave (that had scarred Sally Donovan nicely) or chemical concoctions boiling away on the stove, John took it in his stride. The experiments were what marked Sherlock's territory, and John wouldn't have it any other way. But acid in the bath? That was the last straw.

"Sherlock Bloody Holmes!" John yelled. "Care to explain why my soap just vaporised?"

The frothy foam on the liquid's surface didn't help matters.

As usual, though, John got no answer. With an irritated groan, he pulled his jumper back on and headed off towards the sitting room. Also normal was the figure sitting calmly in his flatmate's chair. Without looking at him, John started searching under the desk for his slippers.

"Try under the sofa," Anthea said.

John stood up quickly. Anthea was sitting in one of the kitchen chairs with an eyebrow raised. John knew he would probably start blustering through a one-way conversation with her if he didn't distract himself.

Then it dawned on him. If Anthea was here, that meant her employer would be too. John stifled a groan.

"What do you want from us this time, Mycroft?"

It hadn't been Sherlock in the chair. The elder Holmes sibling gave John a pleasant smile.

"I am merely dropping by to pass on a few files to Sherlock. I was-"

"Uninvited, as usual," Sherlock interrupted, flinging the door open.

"Good afternoon, Sherlock."

The youngest Holmes brother ignored the greeting. He fixed his expression to look as surly as possible and, taking the shortcut over the table, went to deal with the violently hissing pot on the stove.

"As mature as ever, Sherlock," Mycroft said mockingly.

Pleasantries were never exchanged between the two. John wasn't sure why Mycroft even bothered greeting Sherlock at all. He never responded.

John's attention was then diverted from his contemplations when a resounding crash came from the kitchen. Acting on instinct, he darted forwards. However, Athena blocked his way, eyes still glued to her phone screen.

"He's spilled it on the floor. Looks corrosive. Let him deal with it."

"What is it?"

Mycroft answered for her.

"Sulfuric acid. Sherlock always did love to play with the more destructive chemicals."

Sherlock's sigh of disgust was audible even from the other room. "You handed over the files, Mycroft, which means your business here is finished. Now, if you're going to laze about in my chair and make jokes at my expense then you can show yourself out."

That earned him a patronizing tut.

"As you wish, brother."

John stepped back to make room for Mycroft to walk. He got up fluidly as Anthea produced his trademark umbrella, and nodded to John.

"And by the way, John," he said casually. "Harriet has been detained again."

John muttered a few choice expletives, making even Anthea look at him in surprise. He was usually fairly laid back, but Harry was a special case. Who wouldn't be angry if their sibling was wasting their life away with various addictive substances?

I don't know how Mycroft has refrained from strangling Sherlock. I get close to it daily, and I've only known him a couple of years.

"For what, this time?" he asked tightly.

Mycroft grimaced. "Drunk driving, amongst a few other minor charges. She'll probably serve a short time in a rehabilitation centre."

John knew what he meant. Harry should be getting a prison sentence, but Mycroft was going to pull in his connections once again so she got off lightly. He nodded gratefully. When Harry got out, she was going to have a strict talking-to. But Mycroft had one final bombshell.

"Oh, and your niece will be coming to stay."

John gaped, and he and Sherlock spoke at the same time.

"What niece?"

"John doesn't have a niece."

Mycroft smiled serenely.

"Wrong, dear brother. Anastasia has no other willing relatives, so you have an option: let her lodge here for a few weeks, or I shall see to it that she finds alternate accommodation."

A care home, no doubt, or something similar. John turned to Sherlock, who had started to protest.

"Nonsense, she can't-"

"She'll be welcome here, Mycroft," John snapped, cutting Sherlock off.

The consulting detective shot him an exasperated look, but John glared at him until he backed down. Mycroft looked satisfiedly at Sherlock, who had turned his back once again.

"A little bit of warning," Mycroft said, walking out of the door and calling back to him. "She's a very quiet girl. You might want to keep Sherlock away from her."

Something that resembled a firecracker exploded at Mycroft's feet. He rolled his eyes, then vanished into the stairway. Anthea followed suit a moment later, leaving John to deal with a now stroppy Sherlock Holmes. Stepping over a discarded flask, he made his way into the kitchen.

"So, a teenage girl you've never met is going to be sharing the flat for a month." Sherlock stated, looking nettled. "Do you have the faintest idea what to do with her? Seeing as her existence was revealed all of five minutes ago, I'm surprised you agreed to Mycroft's suggestion."

Sherlock paused for a moment.

"Actually, I'm not. Mycroft is irritatingly skilled at manipulating the lesser-minded."

Sensing that Sherlock was only going to descend into making petty quips and insults, John sighed. Leaving him alone for a while seemed the most appealing idea, and he filled the kettle. It was hard avoiding the sizzling puddle on the floor (which Sherlock was going to have to clear up before Mrs Hudson found it issued a death warrant for him) but John managed to plug the kettle in and escape the kitchen unscathed. Quite an impressive feat.

Back in the living room, he dropped into his chair to think. As usual, Sherlock was right. John hated admitting it, but it was true. He'd just agreed to letting a complete stranger stay with them. What had he been thinking?

It could only go so well.

A/N Chapters will get longer, but I have muchos coursework at the moment and this is as much as I could do without going off on a tangent. Leave a review to persuade me to update quickly...? :)