It is a space outwith space, and Clara Oswald is thinking about time. She's remembering the first time she went to the past — the proper past, not the eighties — and how she'd thought about how everyone she'd met was now dead. They'd been alive then, of course, but she wasn't from then. She was from further along, to the point that she could know she was the only human seeing the past now. The idea of the present had become complicated, then, and one that nagged at the back of her mind more often than she'd ever admit.

She'd asked the Doctor about it once, not long after he'd regenerated. Before she'd zipped around space and time like a Gallifreyan Spirograph she'd felt she had a handle on the present: it was just the time which everybody lived in. Now, though, things were a bit more complicated– one year had passed for her since she first met the Doctor, while almost a thousand had happened to him. Did that mean she was long-dead, from his point of view? He'd responded with something about not believing in ghosts, which is the kind of thing he tends to say when he's Editing.

Clara's been noticing the Editing a lot more, recently. She's known for some time that the Doctor doesn't really show her all of space and time, but — to put it in human terms — gives her a PG view of it. When he evades a question or refuses to open the TARDIS door, it's often because he doesn't want her to discover a particularly horrible fact about the universe. The Doctor is a normal adult trying to stop a child from learning the rude words, but Clara is a normal child who wants to know them all– and by this time, she's put more than a few things together.

Take the vampires. When the Doctor was pretending to be young, he'd mentioned something about a Time War before that Time War, when his people had fought creatures that were more or less literally the ones you could find in a horror film. Now that the Doctor is pretending to be old, he spends more time in the library, and more often than not he forgets to close the door. And so Clara has visited the most ancient shelves and pored over the most foreboding books, and she knows something about that War. She can see why the Doctor Edited, now the nightmares have begun– but the one thing a child never forgets is the rudest word of all.

Vampires, she now knows, fight for more than merely blood. Indeed, it makes more sense to think of them as a conceptual threat than a strictly physical one– and to speak of a war against vampirism rather than vampires themselves. The ultimate goal of vampirism is to make itself a fundamental law of the universe: in a world where it has triumphed, all interactions will be essentially vampiric ones. To some degree, this is already the case, for vampirism didn't fully lose its war. When a banker makes a particularly cruel deal, when a cat delights in devouring its prey, the scars of the vampires are written upon the world. The universe, Clara has learned, really is fundamentally callous, in a manner written right into its skin.

That's not what bothers her, though: what she can't get out of her head are the dreams. Every night now the same old man appears in them, familiar despite his unfamiliar face. He is the Doctor, but of the far, far future– this will be the fifth or sixth time he has worn that face, for he is no longer able to come up with any new ones. His skin is crackled clingfilm against his bones. His movements are as rusty as the console he hammers hands against. Clara has seen the Doctor old and defeated before. No matter. This time he is more old, more defeated. He shouts as blood starts coming through the TARDIS walls.

In that dream the Doctor is defending the Earth — and Clara knows the real reason why he clings so hard to her planet, even though she'll never tell him so — and in the dream the Doctor is losing. There's no sign of this down below; people are still laughing and eating chips as the blackness of space is turning red. But then this sense of normality is itself the Doctor's doing: he's tried very, very hard to make humanity think there's never that much to worry about. This is just the day people realise how wrong they've been.

Clara is no longer bothered by the screams as fanged teeth erupt from schoolchildren and blood spurts from passers by. She no longer weeps at the Doctor's exhausted hammering at the console, each time just managing to rewrite history so that Earth is safe from vampires once again.

What bothers her is simply when the Doctor is. Not The One With The Eyebrows — he's safe in the console room, muttering to himself about sentient spaghetti — but the one he is now, in his own present, in which Clara suspects he hasn't seen her in a long, long time. She can't confirm it, and she'll never know for sure– the Doctor could be anywhen, after all.

But.

But Clara dreams of a future that spills across history, where two races thought long dead both rise again for War. Where horror is unleashed, and where hope is forever lost. Where the laws of the universe themselves drip bright raw red with blood.

It's a future that's a very long way away, for her. But she now knows people all have different times they call the present. From their perspective, her schoolchildren could be long dead and her parents yet to be born. From the Doctor's perspective, he could be fighting another war, locked in battle with an enemy that makes the Daleks look like Care Bears.

There's no way to know. And there's no way to ever be sure.

But she can't stop having the same nightmare. Where each night the Doctor's victory against the vampires grows ever more slim. Where his expression grows ever more hopeless. Where he's so far away from her, and there's nothing she can do. Where it's a trillion years away, and where he needs help right now.

It is a space outwith space, and Clara Oswald is thinking about time.