It's completely an accident, the first time it happens.

(He's over 900 years old, after all; Time Lord or not, a bloke's bound to forget a few things with all that information rattling about, isn't he?)

Fresh off a romp in 1851 London, he's left feeling just a little lonesome—just a little bit, only ever a little bit, can't let that pesky feeling burrow too deep or it will eat away until there's nothing left. And another bout of unmarked time frittered away on the TARDIS, with only his own thoughts for company, sounds about as appealing as covering himself in petrol and running facefirst into a bonfire. So he sets a randomized course for somewhere in the vicinity of Saturn's crowded leisure colonies, sometime between eight hundred and two thousand years from now.

(Sometime, any time, out of time. It doesn't matter. It isn't as if he's got anyone he's accountable to, to explain what he's doing with all these empty hours.)

The time rotor grumbles under his command, and he doesn't spare it any thought other than to wrinkle his nose and press harder. The TARDIS is getting old, just like he is, though at least she's managing to escape the downward spiral of growing sentimentality. At least she doesn't keep opening her mouth thinking that another doctor or a feisty redhead will be there to hear what she has to say.

(At least she isn't plagued by the still-lingering traces of a certain bubbly, laughter-filled blonde.)

He has just congratulated himself on a smooth landing in the dusty space market, followed by an even smoother transaction in which, despite having his arms full of mechanical bobs and bits (might as well buy some spare pieces for that grumbling time rotor while he's on shore leave, right?), he has managed to both hand over his crumpled bills and accept his food without so much as a crumb dropped or a drop dribbled, items shifting in his arms in a subtle but tricky juggle that no one but him will appreciate, when it happens.

"Well, I was gonna ask if you needed help, but it sort of looks like you've got everything covered," a familiar voice drawls behind him, and every single one of the manly hairs on the back of his manly hands and arms and neck stands on end.

Feet shift, pivoting him in place, his body turning before he can stop it, moving to look at her despite all of the approximately thirteen thousand alarm bells sounding in his head right now.

There she is, standing in front of him, blonde hair and broad grin and just a little too much eye makeup. Rose Tyler.

Each and every detail of this moment isolates in painful clarity, the relativity of time hellbent on proving itself through the Doctor's sudden hyper-awareness of the metallic taste of the recycled air and the station humming under his feet as the planet and its colonies careen through space at 9.69 kilometers per second, the tinny sounds of street-musicians playing for coins half a block away, the breeze ruffling his jacket lapels and the tiny flyaway strands of Rose's hair. Rose Tyler, here, in this universe, smiling up at him in a blue tee-shirt and denim skirt like nothing in the world could ever be wrong.

Is he hallucinating right now?

His blood rushes in his ears and a million questions rush into his brain, each of them vying for attention on the tip of his tongue, but he can't even manage to eke out so much as her name before his food slips from his hand and lands on the ground with a loud splat.

Rose laughs and cringes at the mess in front of her. "Sorry! Didn't figure I'd startle you like that—"

"What are you doing here?" the Doctor asks, words tumbling out in a hurried cascade. "Is everything all right back home?" (He tries not to choke on the last word, on the knowledge that her home is miles and universes away.) "Did something happen to the other one?" (He doesn't know how to refer to the metacrisis Doctor, how he refers to himself.)

Rose stares at him. "'The other' who?" she asks. "Who are you talking about?"

When he doesn't immediately respond, because "Who the hell do you think I'm talking about?" seems a tad harsh but his brain can't think of anything else to say, something seems to shift in Rose. She steps back to take a proper look at him—a good, long, proper look—and even though his eyes are locked on her face, wondering about the how and the why and especially the how of her being here, right here, right now, after everything, the Doctor realizes that this is not the Rose that he stranded on a beach in a parallel world for a second time just a few days ago. No, her hair is too short for that, her face still just a little too round, her expression open and full of questions instead of closed and guarded. She's exactly the way he remembers.

This is the Rose that he hasn't stranded yet.

As far as personal timeline paradoxical screw-ups go, this one is spectacular.

"You're different," Rose murmurs.

"You're the same," the Doctor answers before he can stop himself. (Before he can run away, which is what he really, really, really needs to do, but his feet are anchors and his ship is moored.)

Rose chuckles. "Well, of course I am, aren't I?"

It occurs to the Doctor that at some point he stopped gaping and started beaming at her like an idiot. An idiot that's going to scramble both of their timelines like a fork twisted in a nerve cluster.

"So, are we ready to go, then?" Rose asks.

The Doctor does a mental rewind. They're in a space market on the Forty-Third Colony of Great Saturn, in the year 3050, give or take a few months. His younger self is nowhere to be seen. Rose's shirt, bearing a rendering of a cat from an art nouveau poster, is one that went missing, ooh, about three weeks after his regeneration into this form. Three weeks, relatively speaking.

(This is precisely why the Academy so adamantly pushes personal timeline avoidance plotting as an educational requirement, but then again, the Doctor didn't exactly pass that course with flying colors.)

"I left you to get some parts," he remembers aloud. "But you couldn't come with, because of the proprietors' religious superstitions regarding humans. So I left you in a safe section of the market to entertain yourself."

Now she's really eying him. "Are you all right, Doctor? Because all of this happened not fifteen minutes ago, and you're looking at me like you've just seen a ghost."

A memory rises to the surface, a vision of Rose on a windswept beach saying all-too-similar words years ago. (Or is it a year from now?) The Doctor stalls. He can feel timelines tightening around him, slithering into his cranium and strangling his two hearts, warning him about the dire consequences if he makes so much as a single step out of line.

"Everything's fine," he forces himself to say. "I'll be back in about thirty minutes. Thirty, and we'll be on our way."

Rose nods at the gadgets and gears in his arms. "Haven't you already got everything you need?"

He loosens his hold and materials fall to the ground in a loud crash that draws irritated looks from several passersby. "Nope," he says, plastering a smile on his face. "This is all rubbish. It's not what I need at all. In fact, it's so far removed from what I need, that it isn't even on the same continent. I need to go find more things. Different things. Other things..."

The more he rambles, the more suspicion crawls across Rose's face and settles in the creases of her brow. "Is this a weird regeneration thing? Should I be worried about you?" she asks, her hands twisting nervously.

The Doctor takes some deep breaths and pushes his anxiety down. Deep down. As far as it will go. He can't afford to alert her suspicions any more than he already has.

If she figures it out...if she knows...if she tries to warn his younger self...

"Yes," he says, "and no. Yes it's a weird regeneration thing; no, you shouldn't be bothered about it. Don't worry, Rose." He draws in a deep inhale, and steels himself. "I'll be right back for you."

It's only sort of a lie.

He turns to leave before she can protest, trainers stirring up dust as they slap against the ground, picking up in speed the further he moves away from her, until he's running full-pelt toward the TARDIS buried in a back alley a few blocks away. It doesn't matter that members of the crowd protest, that Rose can see him running; all that matters is that she doesn't realize when this is for him, or, more importantly, why he was looking at her like that.

(Am I ever gonna see you again?)

(You can't)

His hearts race in a way that has nothing to do with his running.

The second time, it's a less a matter of an accident than it is of unbridled curiosity.

(What will happen if he sees her again?)

He's just saved a ship full of anxious Bharengan tourists in the year 7074 from an almost certain death-by-space-pirates—doesn't he deserve just a little pat on the back for a job well-done? He so rarely asks for anything for himself. He's currently riding the high of that victory, even if it is just the tiniest bit spoiled by the fact that one of the passengers didn't make it.

(She didn't even have a chance to tell her wife goodbye.)

The Doctor diverts his trajectory from Earth and pilots the TARDIS to Kepler-438b ("Or Earth 2.0," he once told Rose with a wink). This is probably the safest time to visit Rose again, while she's exploring a charming forested area and staying away from atmospheres that could burst her little human lungs. And he knows for a fact that he left her here for a full nineteen hours—knows because he was supposed to be back in two, and she was sure to outline the difference for him. (And protests of "But I had to help the methane revolution of '099!" were only met with a scowl.)

He tells himself he just wants to give her a proper farewell, even if she won't recognize it.

The Doctor lands in a wooded grove, indistinguishable from any on Earth if it wasn't for the white-and-silver leaves whispering gently in the wind, and he can just make out Rose up ahead, talking on her mobile as she strolls through the forest. She notices him instantly, and the corners of her mouth turn up in a broad smile before she ends her call and runs toward him.

The sight of her, smiling and happy and here, hits him with all the gracefulness of a speeding lorry.

(Oh, he realizes with a sinking feeling, he should go. He should really, really go—)

But Rose is too close for him to turn back now without arousing her suspicion, and besides, she's already grabbed his hand and their fingers have laced together and he's not about to pull away. "About time," Rose says. He's already seven hours overdue as far as she's concerned. "What took you so long?"

She does a double-take upon seeing the look on his face; his grin must be ridiculous. "And why are you smiling like that?" she laughs.

It's just good to see you is all is what he wants to say. Or maybe even I missed you. Instead, what comes out of his mouth is, "I can't stay."

"What do you mean? Aren't we going now?"

He forces himself to meet her gaze; she'll know he's lying otherwise. "Soon," he promises. She's rubbing her thumb over his, a little detail he'd almost misplaced amidst mourning the loss of everything else. It's silly and wonderful and he promises never to forget it again. "The business on the mining station isn't quite attended-to yet. I just..."

Wanted to see you. Wanted to give you one last hug. Wanted to say goodbye. Am a completely selfish sod who's all-too-willing to endanger the fabric of time itself just to see you again.

"Doctor?" Rose asks. "Did something happen? On the station?"

"No, not at all, fairly standard as far as revolutions go. Why do you ask?"

She worries her tongue between her teeth. "I dunno. Just doesn't seem like you to check up on me, is all."

Her words twist in him like a knife in his gut. The Doctor steps back, pushes out a laugh, ruffles his hair with one hand. "Am I really so cold-hearted as that?"

"Oh yes," Rose mocks. "You're a terribly cold, cold man who enjoys trips to the space-zoo and cries during Pixar films."

"I said I'm cold, not a monster," the Doctor protests, and they both laugh. Her laughter is just as bubbly and effusive as he recalls, spilling out of her like she can't help herself; he'd preserve it in amber if he could.

He desperately wants to stall for time, but he knows the longer he draws this out, the worse it will be.

(Wouldn't it be sort of worth it, though?)

"Well, I really should be going," he says as brightly as he can manage. "This revolution isn't going to solve itself, if memory serves. The lead general is a brilliant charismatic, but he simply hasn't got the brains for strategy. Someone needs to nudge him in the direction of his lovely savvy sister."

"And that someone's gonna be you," Rose smiles.

"Yeah," he mutters. "It usually is."

This is when he should leave, he knows. Leave on a high note, with this last happy memory, worlds better than watching her kiss his hand-grown copy on a beach a universe away and leaving without saying goodbye.

He needs to say it now. He draws in a deep breath. It's now or never. Say it. Just say it.

(Really, shouldn't he at least ask for one last hug, though? Never mind the suspicion at the back of his head that if he does that, he'll never want to let go.)

"Well," he says, suddenly awkward. "That's it, then. See you around!"

The Doctor turns to leave, cursing himself for his cowardice again, but he hears a soft hey behind him and before he knows it, Rose is tugging on his wrist and pulling him into a hug. She throws her arms around his neck and he pulls her in without even thinking. It's an automatic impulse; he can't help it. Arms circle and hands press and bodies collide, pieces fitting together like a puzzle falling into place.

He remembers the feel of her exactly. Remembers just how she fits against him, recalls how every other hug, just like this one, is just a little too tight and lingers just a little too long to be strictly just-between-friends. He knows he can't afford to lose himself in this moment, can feel the almost-wrongness of this small timeline infraction buzzing gently in the background, but he takes just a second to commit to memory the candy-fruit scent of her shampoo and the way his knuckles curl into the small of her back.

"Really, though," Rose whispers against his neck; her breath is soft and warm and it's almost enough to make him shudder. "What's wrong?"

His arms tighten around her. It's all still very familiar, and it would be so very easy to pretend.

"Nothing," he lies. "Just wanted to see you, is all."

"Big ol' softie," Rose teases.

He smiles into her hair. She's more right than she knows; he really is getting sentimental in his old age. Farewells get harder and loneliness grows deeper and he doesn't want to leave but his time sense is aching like a migraine in the back of his skull.

It's a warning. If he stays, something will change that shouldn't, that didn't. He can't let that happen, no matter how much he wants to.

He steps away and drinks in one last look, memorizing any and every tiny facet of information about her that he can, while he still can—the exact shade of her bottle-blonde hair, the tiny upturn of her nose, the sweep of her eyelashes framing warm brown eyes. The fine lines around her mouth that will deepen into laughter lines someday, in some other universe. The sweetheart shape of pink lips that he should have kissed.

"See you later then, I guess," Rose shrugs, and the Doctor really wishes that was true for him.

He wishes his smile was less sad for her.

"Goodbye, Rose," he says.

If she's still worried, if she senses the heaviness hiding under his voice, he doesn't know. He turns and leaves before he is tempted to stay, or worse, to take her with him. Because he is a Time Lord, and as much as he hates it, as much as it rankles in his veins and leaves a sour taste in his mouth and makes him feel like a creature howling behind a cage of dusty and archaic rules, this is his duty: to uphold the laws of time over everything else. Over anything he might want for himself. No matter what.

Besides—he got to see her one last time.

It will have to be good enough.