There's a lot of things the Doctor doesn't know about Clara Oswald.

He doesn't know how he watched her die twice and still, miraculously, has her: how he can walk into the library to find her dozing in a chair, surrounded by books because she couldn't pick just one to flick through; how he can still take to see the Emerald Deserts of Kormal or to try the many delicacies of the Bessali Belt or even just to wander the streets of Vienna in 1920; how he can feel the warmth and pressure of her small hand in his while they run from whatever's chasing them this week. It bothers him, the not knowing. Terrifies him for a host of reasons. Not the least of which is the thought that she's somehow on borrowed time that's running out. He can't quite decide whether he's meant to have her ("like destiny," he remembers telling a small girl at a park) or whether he was never meant to have her.

He doesn't know how her mother died. She's never offered up the information and he doesn't ask because he understands. He doesn't really want to talk about how his mother died, either.

He doesn't know why she and the TARDIS don't get on. The TARDIS didn't like Jack, but that was different – the instinctive reaction of a being of time when faced with a fact. His own gut feeling, multiplied a thousand times over. It seems different with Clara. More personal. He's caught Clara and the TARDIS both having a go at each other when they thought he wasn't listening. Mostly he just chalks it up to personality differences, but if it keeps on he's considering staging an intervention of sorts.

He definitely doesn't have the foggiest idea why a clever girl like her can't figure out a soufflé.

But he's learned a lot about her, in her short time in the TARDIS. Most of it is utterly useless in terms of Clara Oswald: the mystery but is absolutely fascinating in terms of Clara Oswald: the girl.

He's found that her favorite color is red ("not like a tomato though; like an apple, or a really good lipstick," she tells him once, and he's sure it isn't her intention but he spends the next four and a half minutes thinking about lips and the myriad of things humans do with them), that she requires a cup and a half of tea in the mornings before she starts to form full sentences, that she twists her mother's ring round and round her finger when she's thinking.

He knows that she's quick. Sometimes she knows what he's thinking even before he does; it's kept them alive more than once. Her intuition is often uncannily accurate, and it carries over into more than just saving the world. Even as stubborn as she is, she doesn't often push on sensitive subjects. He thinks she probably knows all about keeping losses close to one's chest, after the way he saw her clutch the book at her mother's grave.

He's also learned that, when she quirks her eyebrows at him and heads down the corridor to her room after yet another close call with death or obliteration or the destruction of time as they know it, he should probably undo his bowtie and follow her.

He's seen the effects in the morning light (or what passes for morning in the Time Vortex, anyway) of his mouth on the skin just behind her left ear or near the tiny, raised scar on her collarbone. When he runs his fingertips over the mottled purple (lightly, so as not to hurt her; he never wants to do that) and apologizes she swats his hands away and laughs, tells him if he's really sorry he'll finally take her to that underwater museum in the Crystalline Sea he's been promising her for weeks now. (He does.)

He's figured out how much pressure from his thumb between her legs will make her twitch and how much will make her clutch at him, almost involuntarily. He's memorized the pitch of the hissing sound she makes when she sucks in air between her teeth, gotten so familiar with the particular curve of her breast that he could map it out geometrically (and there's more than one planet, he knows, on which that could potentially come in handy). He's seen the little cluster of beauty marks on the small of her back, the ones that almost perfectly form the constellation of Vida, in the little solar system of Yi, on the edge of the universe.

(One night in the quiet he tells her the myth of Vida as she curls next to him, hovering on the edge of consciousness. He speaks of a sun who hid away when her twin went out like a candle, and of how the world withered in her absence, and of a woman – Vida – who every day made the trek to her hiding place and tried to coax her out. "Did it work?" Clara asks, sleepily, and he tells her that it did but that Vida burned when the sun comes out and the sun in her sorrow created Vida's likeness in the sky. "I think I'd like that," Clara says, her breath ghosting over his ear, points of heat all along his body where skin meets skin, "to be remembered in the stars when I die." His arms tighten around her as he admonishes her, "Don't you talk like that, Clara Oswald." She's already far more like Vida than she realizes.)

He's not surprised the first time he learns that her teasing translates from one medium to another, becoming physical instead of verbal. She makes a game of it, almost, murmuring "down, boy" against his jaw when he thrusts impatiently into her hand. Later, when he rolls over, using his knees to nudge hers apart, she places a hand on his stomach to stall him and begins tracing lazy patterns on his skin, the light touch making him shiver. "For someone with all the time in the universe, you sure are in a hurry to get on with things," she observes, as her hand slowly moves lower and eventually grasps him, guiding him to her.

It's a bit vindicating to see that after they get properly started she's as eager, as impatient, as he is. Her fingers tangle roughly in his hair to pull him down (god, he's never been more thankful for this incarnation's hair), lips pressing to his so hard he knows they'll both be bruised in the morning. He welcomes the way her breath catches when his hand runs along the length of her body; welcomes the sensations, the tactility of it all: skin and warmth and pleasure and pain and slickness in a single moment.

When he finds just the right angle he takes advantage of it, over and over again, and her nails dig half-moons all over him. Shoulders, arms, hips, arse; a hundred little indents in sets of five, like constellations of crescents on his skin. And then she's moving erratically against him, in a rhythm he can't quite match ("Who's in a hurry now, Clara Oswald?" he manages to get out through gritted teeth, and he thinks it says something that she doesn't even tell him to shut up), and before he can find it again her hips buck one last time and he feels it pulse through her like waves as she cries out. (He files that sound away, in his mind; one more thing he knows about her.) One more stroke, two, three, and then he's there with her, suddenly drained.

They detangle from each other, the Doctor dropping carefully next to Clara on the almost-too-small mattress (he's going to have to have words with the TARDIS about getting Clara a proper bed). He fights his fatigue long enough to carefully push hair, sticky with sweat, away from her face; "You're such a sap," she murmurs, eyes flickering open briefly and a smirk tugging at the corners of her mouth just before she dozes off.

He explains while she sleeps that he hurries because, despite what she thinks, he doesn't quite have all the time in the universe – just most of it. And most isn't always enough.

"Everything ends, Clara," he sighs, pressing a kiss to her still-damp temple as she sleeps and cataloguing away the salt taste of her sweat on his lips as one more bit of knowledge about her to keep when this ends, too.