Ah, I just couldn't resist writing about a younger sister! She's in her very early twenties, still studying (Such a giant age gap, I know!)

Hope you enjoy! :D

It was another quiet day at the Baker Street residence — Sherlock was getting fidgety and John was in his armchair typing away at his laptop, writing up their most recent adventure. It was not even midday and Sherlock had already set the kitchen on fire. Twice. After John had confiscated his blow torch saying that he'd only return it if Sherlock behaved, he resorted to rocking back and forth on the sofa and whining.

"John. I can't take it. My brain. My mind. It's rotting. Give me something. Anything,"

"Check the newspaper, I'm sure there's something. How about that murder in Kensington?"

"The butler, it was the butler," he snapped.

"Wha —"

John was cut off by the ding of Sherlock's mobile phone. The pyjama clad man's eyes skimmed over the text before giving a very small smirk. He jumped up suddenly and started pacing the living room vigorously while muttering some things under his breath.

"What is it, Sherlock? Is it Lestrade?"

"Milk, John! We need milk! And some tea as well!"

"What? Why?" He asked confused while Sherlock made his way to his armchair and pulled him to his feet, "What? Sherlock what are you—?"

John was shoved his jacket and some money and pushed out the door before he could finish his question. With a frustrated huff, he took off for the store, hoping that he wouldn't come back to burnt down ruins of what used to be his apartment on Baker Street.

As John trudged up the stairs, he heard a faint giggle that without at doubt came from a woman. And it was certainly not Mrs. Hudson. With arms full of shopping he walked through the open door and came upon the sight of a young lady in her early twenties sitting in Sherlock's armchair. The source of her amusement seemed to have come from the iPhone in her hand. She had wavy, raven coloured hair that was in a pony tail that fell down her deep purple, sweater clad shoulder. 'She's rather attractive' he mentally remarked. He cleared his throat.

"Oh," she looked up, "Hello Dr. John Hamish Watson,"

"Uh —," he peeped into the kitchen to see a calm Sherlock staring into space in front of another experiment, "Sherlock?"

"Oh, don't bother him, he's gone into his mind palace," she remarked nonchalantly, "He won't be answering you anytime soon"

"Oh, er, I see"

John went about putting the groceries away, very conscious of the mysterious young woman in his flat at the moment. Was she a client? Did Sherlock even know there was a woman in the sitting room? John had come home a few times to nervous clients, confusedly waiting for the eccentric detective to snap out of his mind palace. He was just closing the fridge when dawned on him and he whirled around to face her.

"If this is Mycroft again —,"

She chuckled.

"If it is, you can tell him I am not getting kidnapped again to some unknown place and if he wants to see me or Sherlock, he'd have to come here,"

She sighed, "Oh you really are hopeless," She got up and walked up to Sherlock and gave him a gentle shake.

"What? What are you doing?" he asked a bit panicked, hoping she wasn't going to do something unpredictable to his flatmate.

Light returned to Sherlock's eyes and he looked at John, "Oh, good, John. You're back. Just in time"

"Just in time? What for?"

"Mr. Holmes, I've been waiting here for over half an hour. I don't really think that it is 'just in time' ," She interjected.

Sherlock gave her a slightly confused look.

"Calling me that again are you?" he said annoyed as he turned to face her.

"Oh come on. Would you prefer 'Sherly' ?" she countered.

"I would prefer it if you called me my name"

"Mr. Holmes is your name"

"It's my surname. I meant my given name"

"Why? Afraid that people will know you're related to the powerful Mycroft Holmes?"

His jaw tightened at the sound of his brother's name and John decided to interrupt them.

"No, what? Who are you? Why are you here?" he shouted at the young woman. The day was getting more and more confusing and frustrating. She broke out into a wide grin and Sherlock gave a low chuckle, both obviously amused at his reaction.

"John," he began, "This is my younger sister"