Reluctantly, the Doctor takes Amy and Rory to the beach, as per the mad ginger's request. In his opinion, it's really a waste of time travel. Plus, nothing good ever comes of visiting the beach. Then again, he might be slightly biased.
Nevertheless, they visit the beach - Amy's favorite beach as a girl, just because the Doctor knows it will make her happy, and he likes to give her that - and as Amy and Rory walk along the edge of the ocean, the Doctor hangs back near the TARDIS, longing for an adventure, a distraction, some excitement.
His wish is granted as, out of no where, a girl suddenly launches herself straight into him, knocking him flat on his bum. She quickly straightens, shaking back a mane of bright blonde hair and gazing down at him like a warrior, gun strapped to her back, clothes mussed. As his eyes adjust to the sun, his hearts stop.
She takes him in, frowning in mild frustration but unaffected otherwise, as if she had been expecting him, as she she knows him.
"Doctor," she says, nodding at him, letting the barest smile curve the corner of her mouth.
"I," he falters. Rose laughs, a twinkling, beautiful sound, offering him a hand up; he doesn't take it, doesn't move - just stares at her, wondering if he's started hallucinating again. He used to have the most vivid memories of her, before he regenerated, but since meeting Amy, they've stopped for the most part. Only in his sleep do they haunt him.
He doesn't sleep anymore, though, or at least, it's rarer than it once was.
Rose looks down at him curiously. "Well, here's a sight I never thought I'd see: you, at a loss for words!"
The Doctor stands slowly, brushing off his pants and gazing into her deep brown eyes: they are as gentle as he remembers, as compassionate, as loving, as endless. Stepping back, he says cautiously, "You know who I am."
Rose cocks her head, and the Doctor steals himself against the rush of pain in his hearts; everything about her is too perfectly Rose to be real. "Course I do. You - " Her eyes widen. "Oh. We've never - I mean. You don't...know."
Rose bites her lip, steps backward as if to walk away. "I'm sorry. I - I shouldn't be here. I gotta - gotta go."
The Doctor rushes forward, grabbing her arm, and feels that familiar spark. (So - not a hallucination after all...) "No. Wait," he says urgently. "Why are you here? How?"
"I'm sorry," says Rose. She squeezes his hand gently once, lingering as she pulls herself away. Her eyes grow serious - more serious, more mature, with a quality that (heart-breakingly) reminds him of himself - than he's ever seen her - as she tells him, "I can't be here. Y'know. Timelines and such." Forcing a smiles, she turns and treks back up the hill, and the Doctor lets her go, pushing away all thoughts of grabbing her and hiding her inside the TARDIS for the rest of eternity. After all, she's learned from the best: if anyone knows anything about screwing with timelines, it's him.
"Do I ever see you again?" he calls after her before she can disappear from his life - again - because he can't help himself; he could never help himself when it came to her.
Rose turns back, grinning a little, the hope creeping back into her eyes. "I don't think you'll ever be able to get rid of me!"
Then, quick as she appeared, she is gone.
She doesn't know how right she is.