Rose/AUDoctor.

While dimensional hopping Rose runs into another Doctor. He's cynical, sarcastic, rude, arrogant, and he has no idea why he trusts Rose Tyler so very completely.

She continued down the street, walking casually, like she belonged.

She didn't.

This wasn't her world and more than she belonged to it. But to find him, it might be hers for a night. Tucking her hands into her pockets and hunching her shoulders against the cold. She didn't get her hopes up because there was a small chance she would run into him here. Her calculations weren't always spot on—were rarely spot on. But she tried. And persistence would, in the end, pay off.

Usually she walked aimlessly, heading to where the trouble was. Today was no different. She followed the sirens, jogging through an alley towards the flashing cherries and berries. Rearing back at the sight of fire and hostile alien, Rose heaved a sigh and then held it back as she saw a familiar head of hair bob and weave through the chaos. "Oh Doctor..." She found her in and then dodged between the special police forces to get to the Doctor. There were cries behind her that she ignored as she sprinted through the fire fight, diving at the Doctor and carrying them both to the ground out of the way. "You idiot! What do you think you're doing!"

"What the hell! Get off me! Who do you think you are?" He demanded, thrashing.

Rose rolled off him, grabbed his shoulder and pulled him into cover behind some rubble. "Are you trying to get yourself killed!"

"So what if I was! It's not like it's any of your business! Who are you anyway! I don't need help! You'll just get yourself killed here!"

Her lips pursing and brow dipping, Rose examined his face, the lines harder, eyes colder. "You don't know me."

"No I don't!"

"Settle down, Doctor. I know you. Relax."

He opened his mouth, shut it again, and finally settled on a deep scowl. "What are you doing here? You're going to get yourself killed!"

She grinned. "I know my way around Cybermen and bullets, Doctor."

"Not fair. You seem to know me. What's your name."

"Rose Tyler." She searched his face anxiously, seeking any spark of recognition, but finding nothing. So she rolled her eyes and poked a head above the rubble to find the out. "You don't know me here. But we're going to get out of here. And get rid of those pesky Cybermen."

"Who are you..." He demanded, eyes narrowed, hand sneaking into his jacket pocket, the long coat absent.

"Relax, Doctor," she drawled. "Hold off the sonic. I'm a friend."

"A friend? Oh really."

"Yes, Jesus, you're a prick. The Cybermen aren't looking that way—we can sneak by and then get out. Then where's your TARDIS. We'll make a run and we can figure out how to make the Cybermen retreat."

"Retreat?" His face squinched up in disdain. "Why would we want them to retreat? If we just eliminate them all—b"

"Eliminate! Doctor..." Rose gripped his shoulder. "You don't do that."

He rolled his eyes. "I don't have time for this." And then he was up and running through the escape route Rose had pointed out.

Rose swore under her breath and then shot after him. "Doctor! You're not a killer!" She grit her teeth as he ignored her. "This isn't the way you do things!"

"Oh really!" He shouted, whirling at her as they rounded the corner. "And what would you know?"

"I know! I know you! You're not a killer!"

Something turned over in his chest, but he frowned at her darkly anyway. "You don't know me. And when there's no option left, destroying the enemy is the only course of action."

"You don't mean that." Her hand came out but she let it drop before the touch connected. "Did you ever meet a Martha Jones? Donna Noble?"

"What? No. I have no idea who you're talking about. And we don't have time for this."

"Doctor, people are dying, and we have to do something. Where can we take the Cybermen?"

He rolled his eyes, but the cutting reply didn't make it out of his mouth.

"Come on. You're clever. The TARDIS has a tractor beam of some sort, yeah? Pull them all up and fling them into a black hole or something. That's fine."

"How do you know so much?" He hissed, but he was already grabbing her hand—why was he doing that—and running towards the TARDIS. She couldn't get lost or separated from him, and that was the easiest way to keep ahold of her.

"You great stupid lug, I know you, have travelled with you, and... and all that."

The Doctor skid to a halt in front of the TARDIS, cursing as he tried to fit the key into the lock, finally kicking the door open.

"Hey! You should treat her better!" Rose hurried in after, swivelling and pounding switches.

"OI! What the hell are you doing! No one touches my TARDIS!"

"I know what I'm doing," she hissed back. "You taught me."

She scooted around to the monitor, and the Doctor let her, instead calling to her, "Are we over them? I can track the Cybermen's energy readings and we'll pick only them up."

"Great!"

"Right," he snapped back, not sure what else to say as his hand hovered over the lever.

"In position! Go!"

He flicked the switch and then flew around the console, hands everywhere before he announced they were off to the black hole, as Rose had suggested. It was an option he hadn't thought of. The blonde was clever and sharp, meeting him toe-to-toe. She grinned at him from across the console, collapsing back onto the bench.

"Whew! That was amazing. I'd..." A bereft look crossed her face.

"What?"

"I'd forgotten what a good team we are..." She smiled.

"Huh..." He blinked at her, something a little like awe blooming across his face. "We... You know, we really are!"

She laughed. "Ready to disengage? Black hole in sight!"

"Aye aye, Captain!" He knocked the lever with a flourish and spun around to see her smiling back at him.

"Whoops... I've got to go, Doctor..."

"Go? What? Where are you going?"

"I've got to go back." She held out a hand.

He rushed to it, dread clawing its way from somewhere dark as he grasped her hand. She rolled up on her toes and kissed him lightly. "What?"

"Be good. I know you'll be good. You're fantastic. Brilliant. Clever. And always, oh, always my Doctor. Back to the other side..." She whispered as she suddenly faded from his grasp.

All he was left with was the lingering scent of battle and lilies and a name. And he had all the time in the world to find one Rose Tyler.

The Doctor flicked, banged, kicked, and shimmied controls, sending him back to Earth to begin his search.