This prompt is from barachiki.

Sherlock is an alien, and John is an astronaut.

He's a doctor too, of course, but they need doctors in space.

So off John went, to boldly go, or whatever the phrase was. He's never really been one for travel, whether it was to the coast on holiday, or to outer space.

But here he was.

Here and there and everywhere, on account of the absent gravity. No planet pulling him towards it.

He missed gravity. He missed being wanted by the earth. Gravity was always something to depend on. A mathematical constant. Space was just so random.

So there he was, in his rocket, or space ship, or whatever they bloody called it. (Did he mention that he was mostly forced into this? The world was so desperate for space doctors that those who couldn't afford the schooling were offered free tuition, as long as they devoted themselves to a year of space service. John was regretting his choice, but there wasn't much he could do now.)

Alone, since he was the only one who was getting sent up that date.

(He may have needed to do extra training, but it wasn't his fault dammit, since he'd gotten that shoulder injury training six months again. Who knew there was so much training?)

On his way to the space station, or whatever. He'd learned all the lingo, but was having a bit of a hard time remembering it because he was in bloody outer space.

It was quite a bit unnerving.

At least he didn't have to fly it. It was all computer operated, his one saving grace.

If he'd been forced to fly it, he wouldn't have made it out of the atmosphere. (Which may have been for the best...)

He sat back in his chair and sighed, looking out into the vastness, darkness, emptiness, of space.

Except... it wasn't. There was something out there. Something bright. Something that was growing.

John reminded himself not to scream, even though he was alone. It'll be fine, he told himself, and kept telling himself, right up until the ship started shaking.

And shaking. And shaking.

So much shaking that John worried it was going to shake itself to pieces.

Until it stopped, and he found himself (and hopefully the ship) in one piece.

But there was something else.

Someone else. (Were aliens classified as people?)

Footsteps reverberated throughout the passageways.

John pulled at his seat belt, desperately trying to free himself so he could hide before it got there.

"Hiding won't help," it said with a sigh.

Said. In English. With a bloody accent and everything. Was this supposed to be an alien? Was it a joke?

John peered out from behind the seat he'd crouched behind. (Like that would help.)

"Are you an alien?" he asked the creature, who looked remarkably human, especially considering he'd been in the vacuum of space only moments before. He was tall and lean, sharp angles of bones (or whatever he had for a skeleton), a mass of hair (or something similar) on his head, and the most fascinating eyes that John had ever seen.

"I'm an alien, you're an alien. We're all aliens to someone," he said disinterestedly.

That startled John for a moment. "I don't believe this," he muttered to himself.

The alien shrugged.

"Do you have a name?" John asked. "I don't know... you speak English. You even have an English accent."

"Sherlock," he said, examining John. "And I don't know what you mean about 'English'. I speak the language of my people, and they have spoken it for eons before that."

"Sherlock?" John said, rolling it around in his mouth. It certainly was an alien enough name. "I'm John."

Sherlock frowned. "A strange little name." His eyes twinkled. "For a strange little ma-"

"Don't finish that," John warned.

Sherlock looked intrigued.

"What the hell are you doing on my... erm, my rocket ship?" John demanded, stumbling over the correct words.

Sherlock blinked. "It's not a rocket ship. The propulsion is supplied by-"

John waved a hand at him. "Whatever. I'm waiting for an explanation."

Sherlock shrugged. "I was bored. I decided to wander. Got a little bit stranded, saw you in your space craft, decided to pop on in."

John rubbed his face, processing that.

"How can you survive in space?"

He shrugged. "How can you not?"

"Our bodies aren't built for it," John retorted.

"And ours are," Sherlock replied.

John examined him warily. "You look rather human look, considering."

Sherlock glanced at himself. "I hadn't noticed."

John sighed.

"Our forms... aren't always like this. They can change to suit our environment. It's probably why I look like you, since I'm in a ship that has an environment designed to keep you alive." He smiled. "It's why bubbles are round on your Earth. Most convenient form of travel."

John blinked at him.

"Yeah, sure. Did you want something, like, to take over my planet, steal my ship, kill me and all other humans? Anything along those lines?"

Sherlock looked at him like he was the one who spoke about his form changing.

"No," he snorted. "Whatever gave you that idea?"

"Too many movies, I suppose," he mumbled.

Sherlock shook his head. "I just wanted a ride."

John shrugged. "Sorry, I can't fly this thing. It's all computer operated."

Sherlock grinned wickedly. "I can take care of that."

"What?" John protested, as Sherlock headed towards the panels and began dismantling them with his bare hands. Or whatever. John didn't even know anymore.

"John," Sherlock said, pausing to look into his eyes. "Can you honestly tell me that you want to go to this," he waved his hand around, "space station, and spend a year there taking care of space sickness and complaints of aliens flu?"

He had a point. "No, but-"

"Then we'll go somewhere more exciting."

He knew he was losing this argument. "Like where?" he asked weakly.

"Oh John..." Sherlock sighed happily. "We can go anywhere in the universe we like."

The worry and panic that had been settled in John's stomach for the past weeks faded, to be replaced by something he couldn't quite recognize.

"Anticipation," Sherlock told him.

"What?"

"It's what you're feeling. Excitement, happiness, a tiny bit of worry. Anticipation."

John gaped. "Did you read my mind or something?"

Sherlock snorted. "I don't read minds, I deduce. Of course," he added, "Your mind wouldn't be very hard to read. It's sort of... screaming at me. Could you quiet that down at all? I'm working here."

John closed his mouth and sat in his chair, letting the strange spaceman dismantle his ship, their ship, until he'd finished, replacing the panels back on and looking at John.

"Now," Sherlock asked, his strange eyes glinting at John as he grinned. "Which way would you like to go?"