The prompt for this one was: The Doctor has very recently lost Rose, and considers Sherlock for a new companion.

His hearts throbbed in his chest. It was time. Time to stop being alone. He stripped of his shirt jacket, throwing it into a cupboard door that had only recently appeared on the flight deck of the TARDIS, and had braced himself for what he was about to do.

"Right." He began, "You can't mess me around, alright? I don't need that, I need-"

What did he need?
He'd been travelling alone ever since he'd lost…her. She'd been so real, so human.
Humans, he thought shaking his head, isthereeveroneofthemthatI'llfindeasytoleavebehind?

He knew that this had been different. He hadn't left her behind. She'd been ripped from him.

Rose.Lostforever.

He roared at himself before continuing to speak to the TARDIS.
"Take me to Earth, to London, take me somewhere that's-" He bit off the last word, failing to believe that he could say it.
"To someone fun!"
He grimaced out a smile as the TARDIS obeyed.

That was the day The Doctor met Sherlock Holmes.

It was quiet, for once. There were no gunshots, no shouts of frustration, no sense of danger in the air as John Watson climbed up the stairs to 221B. This, for those who knew Baker Street, was not normal. And John knew Baker Street better than any other place he had lived.

"Sherlock!" He called, opening the door into the living room.

Empty. The front room was empty. But not only empty, cleaned. As though someone had come in, seen the debris that constituted their front room and had organised it.
John gaped for full minute before thinking to check any other rooms.

It was only when he reached the kitchen, after searching his and Sherlock's bedrooms and finding them untouched and normal, laptops and valuables in their rightful places, that anything was different.

Sat at the table was a man. Reading John's copy of Grey's Anatomy.
He was scruffy haired and tall, with glasses on the end of a crooked nose, striped suit contrasted with a rather battered looking pair of Converse trainers. Hearing John enter the man turned to face him and his face split into a wide grin.

"Hello there! You must be John! Sorry I let myself in, and helped myself to your papers, -well I say let myself in, don't look in the airing cupboard- I was just looking through some of your books, I find it helps to remind myself of the human nervous system sometimes. But yes, ah no need to point that at me, I'm the Doctor!"

This speech had disarmed John somewhat. He had expected the stranger to insist he wasn't a burglar and beg John not to shoot him. He lowered his gun and looked at the man with utmost confusion. The gun hadn't phased him, he hadn't even stood up. After finishing his speech he returned to Grey's and said calmly,
"Any chance of a cuppa?"

OneofSherlock'sfriends. John mused, convincing himself. Asifonelunaticisn'tdifficultenoughtokeepundercontrol.

"One lump or two?" John heard himself ask.
"Two please."

It struck John how very bizarre the situation was. So he ignored it and sipped his tea. He was still sat with the strange stranger (for that's the only way John could describe him) fifteen minutes later when Sherlock bounded into the room.

"John, I've got it, the restaraunt has a bunker beneath it-"
His stopped dead as he took in the sight before him.

John, calm, tea in hand. Sat opposite a stranger, John's book held firmly, toothy grin splitting his features.
"Mr Holmes!" The stranger began, "A pleasure to meet you! I've heard so much about you! I've always wondered, how do you-"
"John. Who is this?" Sherlock snapped. John gaped absently.
"Buggered if I know Sherlock! I though he was a contact of yours!"

The stranger had bounded up to Sherlock, peering at him with awe and interest. His hands flapped a little as it seemed as though he was restraining himself.
"Do that thing you do! Where you know everything about a person, go on!"

Sherlock favoured the man with a withering glance, before beginning.

"You're older than you look, a lot older, you're used to people looking up to you and thinking you know what to do and quite often you get tired of it. Well travelled, but you don't find much use for money. Intelligent, and you know it, and you enjoy others knowing it too. You've come here for something specific, either to speak to John or I, but how I'm not sure." Sherlock narrowed his eyes and glanced at the stranger again before stalking into the front room, calling over his shoulder, "And though you've never married you've had love and lost it." He paused briefly. "Recently. You're also an alien."

The stranger didn't move, just turned to John and made an impressed sound, before adding
"I love it when he does that!"

He followed Sherlock into the front room where he had proceeded to "rearrange", or more accurately kick, the tidy piles of papers and books that had been so neatly stacked.
"Ah yes, sorry about that, didn't want to leave it in such a mess once I'd finished with it." The stranger intoned.

"No, I'm sorry," John broke in, staring transfixed at both the stranger and Sherlock "what the hell is going on! Who are you?"

"He's The Doctor, John."

Understanding dawned on John's face, and Sherlock smirked at the round "o" of surprise on The Doctor's face. "How do you-"
"We've met before." Sherlock said. "You said you'd, well you," he gestured vaguely at the suit-clad Doctor, "would come back for me. But you haven't met me yet. Where did you park the TARDIS?"
"Wait," broke in John, "it's not parked in here is it? In the flat? Because what if you said was true Sherlock then-"
John's sentence ended abruptly, as he went to check the airing cupboard.
"FUCK!" came a loud cry.
"I hadn't met John when we first met Doctor," Sherlock smiled fondly, "he's yet to experience the TARDIS. You always said you'd be back when you needed an adventure. So," he paused again, looking into the lost Doctor's eyes, "Rose is gone?"
"Yes." The Doctor rasped, finally getting to grips with the man who already knew him, "She's gone. And now I don't want to be alone anymore." He glanced away from Sherlock, "I need someone with me for a while. Just a little while. Long enough so that I don't feel it." He turned away from Sherlock, perplexed and wondering how much he knew about the ache in his hearts, and merely said "It could be dangerous?"
"More dangerous than last time? Hardly." Sherlock chuckled. "Anyway, that doesn't work on me. No Doctor, what I want from you is a favour."
The Doctor's eyebrow quirked in query.
"How does catching Jack the Ripper sound to you?"

Another yelp came from upstairs,
"SHERLOCK. IT'S BIGGER ON THE INSIDE. WHY IS IT BIGGER ON THE INSIDE?"

The Doctor laughed as he led the way to the TARDIS.

"Sherlock, that sounds like an adventure. Alons-y!"