Sorry if I'm messing with classic Doctor Who/UNIT canon... hope it doesn't offend you too much!

WILD HORSES

"The funny thing is," the blonde was saying. "The Atmos thing? That little problem actually got solved much more efficiently in this world. 'Course, I suppose that depends upon who you ask. The Sontarans aren't best pleased with the outcome here, I'm sure."

They were sitting on the front steps of Martha's flat. Martha had stopped short of inviting the woman inside. She felt sure that if this person intended to do her, or anyone else harm, it wouldn't matter whether or not she was allowed inside Martha's home. Still, she didn't want something or someone who felt so wrong to be in the place where she lived and slept and dreamt.

"How do you mean, in this world?" asked Martha.

"You know about alternate time lines, don't you? Parallel worlds?"

"Yeah, I know that much," Martha said. She chuckled a bit. "You know that I know. By now I've worked it out, you must know who I am and who I work for. So why don't you tell me who you are? And why you always wear the same clothes?"

"I know who you are, Martha Jones," the blonde said. "I know that you live in this flat here, and that you work for the Unified Intelligence Taskforce."

"Well, hallelujah, a welcome bit of honesty."

"You're the daughter of Francine and Clive, sister of Letitia and Leo. Came first in your class at St. Andrews, began medical school four years ago, took a year off to travel, and were accelerated through the final year by UNIT because of your field experience," the woman recited. There was a pause. "And I know that you're engaged to Tom Milligan, that he's a doctor who's off travelling right now."

"You need to leave Tom alone," Martha said, quite seriously, without sounding particularly menacing.

"But he's not the only one, is he?"

"The only one of what?"

"The only one who's gone off travelling and has left you behind," said the blonde, her voice not unsympathetic. "Not even the only doctor you love."

"You are treading in very tetchy waters," Martha said to her, her voice clear, her eyes hard. "You are a total stranger and I don't need this. So if you're not going to tell me why you're here, why you're bothering me and why people keep looking at my back, then I'm just going to go..."

"None of that was supposed to happen."

"None of what?" Martha asked, suddenly standing down.

"The flat, the job, the fiancé," said the woman. "None of it."

"Why not?"

"There was a time, Martha," she began. "A world, really. Where everything was different – you didn't have any of that."

"Great," Martha sighed. "Sounds like a magical place."

"No, but, you had so much more," the woman said. Tears came to her eyes. "You had..." She swallowed hard.

"What?"

"You had the Doctor."

Martha sighed and leaned back on her hands. "I should have known that's what this was all about," she sighed. "For your information, I never had the Doctor. He had me. I travelled with him, but... he never even looked at me twice."

The blonde was crying, tears were falling like rain, but she worked to maintain a steady voice. "Not in this world, no. But in an alternate timeline, yes, you did. You had him, and he had you. You were never meant to walk away from him, Martha. You said you were going to go, but he was supposed to ask you to stay, and you agreed. And he fell in love with you."

"No," Martha said, standing up. "He didn't."

"Yes, he did," the blonde insisted, raising her voice for the first time. She stood up as well. "Believe me, I wish it weren't true, but it is." She paused as the tears fell, and she caught her breath. For a brief moment, Martha thought she might be choking.

And suddenly, from the look in her eyes, from the hurt she clearly felt at this revelation, Martha was able to see. She let a few moments pass, contemplating whether to voice her thought. At last, "Rose?" she asked, tentatively. "Are you Rose Tyler?"

The blonde woman did not answer, nor did she deny. Her silence spoke volumes, and suddenly, this encounter became a wholly different affair.

"This isn't right, Martha," Rose said to her, in lieu of answering her question. "Time has splintered. That thing on your back..."

"The scarab," Martha mused.

"I can't really see it," Rose confessed, wiping her tears. "I know it's there, though. I can hear it sometimes, and it carries an energy signature. Apparently, it vascillates on a frequency that's out of this time and place – that's why people who are slightly out of their element can sense it."

"What the hell is it?"

"It changes the world in tiny little ways," she tried to explain, sitting down on the step once more. "Small decisions that we make, turning right instead of left, calling later instead of now. But it made the Doctor think twice about uttering one little phrase: Martha, no. That's all he was supposed to have said, and with those words (and many, many more) he convinces you to stay. But the scarab, it changed his mind, held his tongue for him, whatever. And the consequences... well, they're important to re-write. To you and me, anyway. We have to put time back on track."

"Back on track to a world where I stay with the Doctor forever, and he loves me?"

"Yes."

"That is our goal. Not to slay a dragon, not to unplug a black hole or something... the goal is for him to fall in love with me. Nothing greater than that?"

"Nothing greater? That is the greatest thing, the most important thing ever! Greater than you know, Martha... and that is saying something. The goal is for the two of you to be in love, and be together for a long, long time. It needs to happen."

Martha couldn't help but feel her cynicism, sarcasm take over. She sat down next to Rose and turned her hands up in wonder. "You want to put the world back into a position where the Doctor is in love with someone who is not you?"

Rose swallowed hard again, and pushed a strand of hair out of her face. "Yes."

"Why? What's at stake? There has to be something! Earth in peril? Universe dying?"

"Yes, but every single universe is in danger," Rose said. "Something's coming from across the stars to attack them all, but the Doctor will save the universe whether you're with him or not. That's not the question."

"What happens if time takes its course from this point now? The Doctor saves the universe..."

"...but he won't be able to save himself or Donna Noble."

Martha's heart sank. Sometimes the greatest disasters were the small ones. The Earth would be safe, but the Doctor and Donna would perish somehow.

"They don't die, not for a long time. Something worse than that will happen to Donna," Rose told her. "And it will break the Doctor's hearts, and he'll have no-one." She choked a little, and Martha could see her holding back tears.

"Oh God," Martha whispered.

"He'll be so broken that he goes off on his own, turning away any and all company or help. He'll be isolated. He'll transform. He'll have no one to stop him doing things that he'll regret, and it will set some things in motion... he'll have to die on his own, regenerate into a new man with no-one by his side. And all too soon, Martha."

"But isn't that the hazard of a Time Lord travelling with a human? We die, and he's left to mourn for another hundred years or so. What's to say the same thing won't happen to him when I die?"

"The natural order of things says it," Rose told her. "Donna's demise is not a death – it is an unnatural and brutal removal from his life."

Martha couldn't believe her ears. She stood up and paced back and forth in front of her steps for a bit, and Rose just let her process. It was too much. It was wonderful, but too much. "How do you know all this?"

"My world is running ahead of yours," she said. "I work for an organisation that has this weird technology... we've been able to take advantage of the coming darkness. The walls between worlds are breaking down and we can see things."

"I can phone him right now," Martha said. "I can get him back here."

"No, it's too late now," Rose said. "Events that will bring down Donna Noble are already set in motion, and once that happens, the Doctor is lost. We need you to stay with him, to agree to continue to travel with him. That way, Donna doesn't come back into his life, things go differently, he falls in love with you, and he's a different man. He's less reckless, he lives longer, he's happier for a longer time. And Donna gets to live a normal life with all of her fond memories of her one afternoon with him. And you? Well, you win the grand prize." Rose said this almost bitterly.

"Why don't you just take yourself back there? Fix whatever went wrong that forced you to separate, and save him the pain of losing you. That's the biggest sore spot for him, at least when I knew him it was. Heal further wounds – travel with him yourself. Why aren't you contemplating that?"

"I have contemplated that. And contemplated it and contemplated it, but it doesn't work. He doesn't save the world from the Empress of the Racnoss nor help catch the Plasmavore on the moon, who'd be set to wreak all sorts of havoc on the galaxy," she said. "Not to mention, she would have nuked the Earth. And the Master? That's all you, Martha. You were meant to have that trek across the world, not me.

"Besides," Rose continued, now not looking at Martha, but into the distance. "In order to do what you're saying, I'd have to cross my own timeline, somehow get in that room at Torchwood and save myself from falling, or stop my dad from... and, well, crossing one's own timeline? A paradox waiting to happen. I tried it once with the Doctor and it caused a whole heap of trouble. These dragon things came and ate him... it wasn't pretty."

Martha waited. She had the feeling that, at this stage, Rose was no longer exactly speaking to her. She was rationalising, reminding herself again why she couldn't have what she wanted.

"No," Rose said. "It has been made very clear to me that my involvement with him must end... when it did. Believe me, I've explored every possibility. If I could go back..."

"I get it," Martha interrupted. And she did get it. "Are you sure about this?"

"I'm sure," Rose assured her.

"This is for the Doctor," Martha said.

"It is."

"What do I need to do?"

Round the corner, men in berets waited in a Jeep. Martha recognised them as UNIT officials, and opened her mouth to ask, indignantly, what the hell was going on, but Rose shushed her. "Top Secret Ops," Rose whispered. "Not even Colonel Mace knows – don't feel bad."

As the Jeep trundled out of town and across a bit of heath, a million thoughts travelled through Martha's mind. Not the least of which, of course, was is this woman completely mad? But what if she wasn't? What if she was right, and time had been splintered, and she was meant to live a life of love and adventure with the Doctor after all? She had long since stopped daring to dream, but, she noted, it was telling that she agreed to climb into a Jeep with a virtual stranger to help the Doctor, without even giving a second thought to her life with Tom. Compared to what Rose said she could have, this life was a farce anyhow. She could see that everything she'd be giving up would be far superceded by everything she'd be gaining. Or at least that's how it looked.

Next to her, Rose was stoic. Martha tried to think of something to say, but she could come up with nothing. There was so much tension here, so much to hash out, and yet, what difference would it make now? This was Rose. The Rose, in whose shadow she had lived for two years, pining after a man who loved this woman. And now, this very woman said she wanted Martha to be with him, that it was their destiny, and she'd been pulled across universes to bring Martha what was undoubtedly a very painful message for her. In her position, Martha wasn't sure she'd have Rose's mettle.

Then again, it was all in the name of helping the Doctor, saving him from himself. Put in that light, Martha felt differently; clearly either one of them would do anything for him, therefore, perhaps she would have the mettle.

No-one said a word until after Rose had thrown aside the plastic curtain of a makeshift warehouse (really, an uglified circus tent) and one of the officers saluted in response to her authoritative plunging inside. "I've told you, don't salute," Rose said.

Martha smiled inwardly. The Doctor had recently had a similar conversation with a UNIT officer.

The officer, a severe-looking black woman, turned to Martha and said, "Dr. Jones," and offered her hand.

Martha's eyes narrowed as she shook hands with the female officer. "Do I know you?"

"Captain Erisa Magambo," she answered. "We met briefly during the Polturian Sling debacle. Thank you for doing this."

"Er, sure," Martha said, uneasily. She glanced to her right, and Rose was fiddling with some dials and buttons near a pane of computer screens.

"Is it ready?" Rose asked Captain Magambo.

"Ready as it's ever going to get," Magambo answered. "It's a bloody mess."

"Well, it's the best we can do," Rose sighed. She turned to Martha. "You're going to like this. Come look."

Rose threw a curtain aside, and a semi-familiar sight greeted them. A control board with a cylindrical column of light was sitting in the middle of a circular, tunnel-like device. It had familiar dials and handles, a yellow defence switch, plugs and ports for all manner of attachments.

"Is that...?" Martha said, pointing at it. "Oh my God!"

"Yes," Rose laughed. "It's a TARDIS console. But, like the Captain said, it's a bloody mess. Back when the Doctor was working alongside UNIT, not in an official capacity anymore – much later than that – the TARDIS was blasted somehow and the console was sort of destroyed. It crashed to Earth and healed itself... grew new parts. UNIT stowed this thing away, and they've been working on reviving it."

"Wow," Martha breathed, walking around it, touching the edge of the console. "What's with the tunnel thing?"

"That's the teleportation device from Luke Rattigan's inner office," Rose told her. "They salvaged it after the castle went up for sale. It seemed to solve a lot of problems for us. The console here, it can give us reasonable time coordinates and some temporal flux – I mean, it's been disconnected for years, it only carries traces of the vortex now – but we had no kind of pod to travel in, no teleportation ability. But voilà, thank you Mr. Rattigan."

"Wow," Martha repeated. She stole a glance at Rose, who was wistfully running her hand over the defence switch, ghosting her fingers over places where the Doctor's had been in centuries gone. She was remembering. Martha had seen that look on the Doctor's face a hundred times, in moments when she suspected he was thinking of Rose.

"Rose," Martha whispered. "You must have been dragged across universes by wild horses."

"How do you mean?"

"How else could you do this?"

Rose stared at her with steely sadness, but did not respond to her question. Instead, she began speaking again about the errant console. "The catch is, we think it's only going to work once," Rose said. "So we have to be very, very sure."

"About what?"

"About where you're going and what you're going to do there. Now, this little... well, TARDIS has worked very, very hard to track down the moment of intervention at six minutes past two, on the day when you and the Doctor parted company. He nearly said, Martha, no, but he didn't. The scarab made him hesitate. But he needs to say it, it's very important, otherwise you'll leave."

"Got it."

"What the TARDIS, nor anyone else here, has not been able to work out is how we'll get him to say it," she said. "We know the moment, we just don't know how to get into the Doctor's head."

"Okay, so..." Martha shrugged, as if to ask so then why did you bring me here?

"Okay, so..." Rose echoed. "You were there, in that moment, Martha. What was being said? What was the look on his face? How did he react to you – his body, his eyes, anything you can remember."

"Well, I told him about my friend Vicky, and he looked sort of..."

"No, don't tell me," Rose said, her eyes scrunching against her will. "What's important is that you know. Because if you can work out what he was thinking based on all those things and what had been happening, then maybe you can work out how to change his mind."

Martha circled the console a bit more, touched the edge, tried to imagine this archaic-looking thing in the Doctor's world.

After a long while, Martha said, "Maybe I don't need to know what he was thinking," she said. "Maybe I just need to get him alone."