This is slightly crack and very, very AU. Idea from the lovely gifs of: could be anything therefore nothing (remove spaces) and wittyinthetardis over at Tumblr.
John Watson entered 221B Baker Street in a huff after yet another night left stranded at a crime scene when Sherlock spontaneously had a breakthrough which required him to be on the other side of London sniffing a certain clump of grass. He brushed past Mrs Hudson in the hall and stumped upstairs, trying not to slam the door behind himself like a teenage girl who had just returned home after being stood up and who was retreating in a fit of teary rage to her room to write an entry in her diary and eat a tub of ice cream. Because that was certainly not what John Watson was like.
He pottered about the kitchen in drawer-jerking, cupboard-snapping irritability, brewing himself a soothing cup of tea and grabbing the biscuit tin to withdraw to the living room table, opening his laptop and logging onto his blog with aggressive jabbing keystrokes.
John spent the first hour typing up an account of the night with more sarcastic jibes at Sherlock's taste in expensive suits, hygiene habits, and general person than normal, chewing moodily on jam biscuit after jam biscuit all the while.
By half way through the second hour John had calmed down somewhat, and was now merely refreshing his blog repeatedly to see if Sherlock would deign to comment via his phone. He finished the jam biscuits.
The fourth hour came at midnight roughly. John had been engaged for some time in argument with his sister via blog comments, mostly focused, as usual, on defending his sexuality and masculinity.
At one thirty John started checking his phone. No messages from Sherlock. It wasn't entirely unusual for the man to be out until the early hours of the morning, but usually John was with him.
At two o'clock Harry finished the argument with, "calm your rage little brother and stop stuffing your face with jam LOL I'm goin to bed", to which John maturely replied, "stuff you I haven't been", as he opened another packet of jam biscuits with his teeth.
Three o'clock found John pacing up and down the living room, fiddling with his phone and trying to restrain himself from sending Sherlock a text. He concentrated on not thinking about that time he had gone out on a date with Sarah and had returned to the flat the next day to find Sherlock lying on the floor passed out after stumbling in at God knows what hour with a broken rib and a bloodied nose.
Worst of all, he was starting to feel like the jam biscuits were going to make a reappearance soon.
Finally at a quarter past three there was a muffled knock from downstairs, barely caught by John as he passed by the door on his way round the living room. He swore in what was very definitely not relief, muttering loudly as he made his way downstairs.
"And he hasn't brought his bloody key with him again, has he, no, just assumesthat I'm going to be up waiting for him to let him in. Well, next time I'm not bloody well answering the door even if I am up waiting for him and he can freeze to death for all I care … Swanning off and leaving me in a mansion with three dead bodies hanging from the ceiling and Anderson giving me the evil eye … And then coming home at some ungodly hour – You are bloody late!" John shouted as he wrenched the front door open, and then stopped quite suddenly when he realised that it wasn't Sherlock at all.
"Am I?" said the man standing on the doorstep, with a soft, bashful sort of grin, rather like a chastised but cheeky schoolboy. It stood at odds somewhat with his appearance; a youthful, fresh face and lean body in brown trousers and tweed, a bowtie secured at his collar. "Sorry, I'm always getting my dates mixed up." He winced slightly to himself, adding, "they always get so annoyed with me. Well, she does. Did. Will do."
John floundered for words for a brief moment before recovering.
"Erm … I'm … I'm so sorry, I thought you were my flatmate," he said.
"Don't worry, easy mistake to make, I mistake people for my flatmates all the time," he said cheerfully with another bright smile and lifted eyebrows, "well, some of the time. Well. Never."
John blinked, giving the man a sidelong glance.
"Sorry, can I help you at all?" he said tiredly.
The man grinned, "I just came to check in on an old young friend of mine."
"Sherlock? He's out at the moment, I'm afraid," explained John rather testily, "if that's who you're looking for; Sherlock bloody I prowl the streets for criminals when all the normal people sleep Holmes."
"Yes, that would be him," nodded the man, "though I knew him as –"
"I told you to stop calling me that, Doctor," rumbled a voice coming up the pavement. John stuck his head out the door and glared at the speaker.
Sherlock looked unperturbed by John's Death Glare of Death and Capitalised Doom, pushing past the man at the door and John and making his way upstairs, a clear bag filled with what seemed to be several mouldy clumps of moss and grass swinging from one hand.
"Let him in, John," Sherlock called back over his shoulder, "he'll only find another way in anyway and I don't want another materialisation scenario otherwise Mrs Hudson will think that there's some construction work going on upstairs for all the sound it makes."
He disappeared upstairs and John stepped aside begrudgingly to let the man in. He smiled blithely at John.
"Glad to see some people never change," he said.
"No, he doesn't," sighed John, and lead the way upstairs.
They found Sherlock in the kitchen, coat off and sleeves rolled up to his elbows, dropping clumps of grass into beakers.
"So what do you want this time? I'm perfectly fine, before you ask," he said without looking up.
"Good," said the man, "that's good. I'm fine too."
It sounded strangely rehearsed for some reason, and Sherlock's eyes flicked momentarily towards the ceiling.
"This just a 'social call' then is it? I can't wait to see what extraterrestrial being is going to invade this time."
"Hey!" said the man defensively, stuffing something silver and green back into his pocket hurriedly, "I'll have you know that I am perfectly capable of visiting old family friends without bringing alien doom with me."
"I've yet to see evidence of that –"
"Woah, woah, hold on," said John, waving a hand. Two sets of sharp, intelligent eyes turned upon him and a lesser man would have stepped back under the combined force. "What's going on? Sherlock?"
Sherlock sighed and tossed down his bag of grass.
"John Watson, this is the Doctor. The only man in the universe who likes to refer to himself as my 'friend'. Doctor, this is John Watson, also a doctor, and my flatmate."
"I'm sure you have plenty of friends, St –"
"No one says the word 'friend' quite in the way that you do," said Sherlock, his tone making unclear whether he was distasteful or exasperated. "In fact whenever someone talks about a 'friend' of mine I automatically assume they mean you. The word has taken on unpleasantly Doctor-y connotations." He glared at the man and resumed filling the grassy beakers with water and chemicals. "Though never mind about my concern towards the invasion of aliens – I see one already has."
"What do you mean about aliens?" frowned John.
"Never mind," said the Doctor hurriedly. He looked about the living room with an air of pleasant interest. "Nice place. Terrible wallpaper – though I like the smiley. Cheers the place up quite a bit. Ooh, checkmate!" He darted over to a chessboard in the corner like a child who had just spotted some cake.
John stepped towards Sherlock, hissing under his breath to him, "Sherlock, who is he?"
"A friend of my father's," said Sherlock. "They flat-shared for a bit when my father was a young man."
"A friend of your father's?" said John disbelievingly, "Sherlock, he looks about nine."
"Gross exaggerations are not becoming on you, John."
"You know what I mean," John gestured over his shoulder at the man who was now absorbed in what sounded like re-enacting parts of Romeo and Juliet with the chess pieces. "He can't be thirty!"
"He checks in on me from time to time," said Sherlock nonchalantly, as if John hadn't spoken. "Usually brings aliens with him."
"I heard that!"
Sherlock and John turned around. The Doctor was looking at Sherlock in disapproval.
"It's true. On my fifth birthday you crashed through the dining room ceiling wrestling a Venusian and landing in my cake."
"That was a mere miscalculation to do with confusing 'cake' with 'lake' –"
"On Christmas when I was twelve you tried to give me a pet that had five limbs, three tails, and bright green feathers."
"I was being nice!"
"Explain the cybermen in my rehabilitation centre then."
"You needed the distraction," said the Doctor, and smiled a small, sad smile, his eyes lifting to Sherlock's with some very old and very gentle emotion in them.
Sherlock was silent. He looked down at the floor.
"This really is a social call this time," the Doctor added, stepping tentatively closer. "I'm just checking you're … fine."
"I am fine, I told you," said Sherlock, a slight petulance staining his voice. His eyes flickered inexplicably towards John. "Everything's fine."
The Doctor's smile brightened ever so slightly.
"Good to hear it." There was a slight pause. The man fidgeted on the spot then started for the door. "Well. I'd best be going then, if you're all fine. I've got things to see, things to have seen, fixed points in time to wiggle about. Love to No-Longer-Not-Mummy and Mummy. And Cakemuncher the Terrible. Always nice to see you, St –"
"I'll show you to the door," said Sherlock, and John watched in bemusement, waving slightly as the Doctor was pushed out the door and down the stairs.
When they reached the front door and the Doctor stepped out into the early morning air, Sherlock could just make out in the dawn the blue police box parked very inconspicuously across the street. He tried not to smile at the familiar sight.
"Well, off again," said the Doctor, smiling up at him, "This has been a short visit."
"You're getting better at them," commented Sherlock with a slight, amused quirk of the lips.
The Doctor laughed and there was another small silence.
"John seems nice," he said after a moment. "Could use a sturdy bloke like that around again."
"You're not stealing him for your collection," Sherlock said a bit too sharply.
"No, I …" the Doctor smiled sadly again. "I think I've stolen enough."
"You've done well so far," said Sherlock not so harshly. "You've managed to refrain from stealing me."
"I liked your father a lot. Wouldn't do that to him." The Doctor smiled up at the still faintly starry sky. "The parents have it the worst, I think. The ones who get left behind. He's my mate. I couldn't."
"Then you should probably stop justifying yourself and keep this to a short visit before you make an offer I can't refuse," said Sherlock quietly.
"I've given you a taste for the lifestyle, though, haven't I," he continued, a slight bitterness in his smile. "All that running."
"My nature and the things I do because of it aren't your fault," Sherlock retorted, "don't be so inflated to assume I wouldn't have been a junkie for adrenaline or anything else otherwise. Things have happened the way they have, and I'm the way I am, and I'd rather be this way than an idiot like everyone else."
The Doctor laughed at that.
"Still peasants are they?"
Sherlock smiled in spite of himself.
The Doctor turned to his box then, smile not so sad. He spun on his heel, jacket flying, just before crossing the road, and waved to Sherlock.
"Catch you later, Stormageddon," he grinned, "keep an eye on those stars."