'What do you know,' said Liz, 'about temporal theory?'

She was chipper enough, at first glance. Second was more dubious… Patsy knew how Liz looked when she was genuinely excited about things, as tired from work as she was, and when there was something on her mind. 'Are you sure of having this conversation at 1 a.m.?' Patsy asked, playfully exasperated, but it would be entirely predictable for Liz to brush that off. She'd met some other researchers like this, you could never drag them away from explaining an insight on something.

When Liz nodded, she continued. 'Well, I know we're aware of alternate timeline versions of people.'

'That's about right. But what makes some of them connect to here and not others?' Liz sighed. 'And there are other questions. How do human minds even make sense of all that? We have documentation of people remembering things they weren't there for, not in our timeline. The Kingdom case, for one. Torchwood might have something — if they only weren't so goddamn uncooperative!'

'Oh, the time I've wasted keeping them off our back.' Patsy smirked and put her hand on the table; there were stale breadcrumps on it. 'What kind of connection? You're going to need something more specific than that.'

'Well,' Liz took a larger sip of her coffee, 'recently I've been having a very peculiar nightmare.'

'Really.'

A bird cawed outside the window.

'I'm on a moonbase somewhere. I think it's the one we were building, in the eighties —'

She explained, levelly. Liz was always good at being composed, more than Patsy sometimes, for all she had been in surveillance. But a nightmare shouldn't have been a crisis to be composed about. Or, not most of them. Of course everything could be compromised, every gap, every channel. Security mindset, she heard it called.

'— we're isolating everything we can. Do you know how sulfiric acid smells?' Liz shook her head. 'And the bodies.

'It was the aughts, I felt. So the timeline — I hope we've just avoided this. I-'

Liz checked, of course. When she visited the moonbase for other reasons, it- Unfinished, not as much as she'd expect but some. And where there was the console and Agent Yellow, just rock. Cycles? How do loops within cycles work? She'd handed off command to Giles in half a daze, later, a bit grateful for a grounding, though not- 'trusted friends' wasn't quite right, though Giles was a personal friend, after years, but that wasn't the point. Liz liked the thing PROBE was doing, that was all.

It was- what the hell- it was like swimming. She didn't even remember being dragged through these corridors, or dragging herself, who knows with how dreams are usually like… But she remembered remembering, in a sense- no, not quite that. As if she could feel the shape where the memory was supposed to be. Guess at its contents by its contours…

'Supposed' doesn't mean anything, she remembered saying once. There's duty, and choice, and the laws of physics. That's all. It was to a psychic, a boy of twenty or so. He worried about what a sure future meant, if there's anything here to follow, or to avoid, or what's even possible… Liz wouldn't separate the three concepts, anymore. She lived within this physics, though she was sure there were others… She'd choose what she'd choose, so she was in a world where she would choose it. (Maybe the TARDIS could shift between those. You wouldn't even need too many new dimensions for that, though she'd never gotten to hear it properly explained, to be frank.) Tug on the strands of fate from her end: same information either way, right?

Or did it happen in this timeline? She should check that, too. The name should be in PROBE's records somewhere.

'So.'

'Yes, I asked Az, he was willing to look around for me. Nothing!'

Patsy leaned back in her chair; it squeaked. 'Okay, I trust you, Liz, maybe this really is professionally interesting. But I don't think we can keep burning PROBE's resources on it.'

'Huh. Nothing for it, then.' But continuing to wonder if she would-

She laid on her back, listening to cars roll by. Had to remind herself she wasn't dead; held her left thigh in her hands, quietly as she could, examined details of its skin to make sure it didn't change when she wasn't looking.

So many people. How-

It's not like it was new. But it hit her like a hurricane, though it wouldn't have then… She was trying to research it, she was trying to know. Doesn't remember how it turned out. Army — threats?

Science, the science she trusts, the social process of people checking and rechecking and working together for that: holding that 'the end' can't justify 'the means' — Liz, explaining all that to some doubtful Silurians, back when she was still at UNIT, though not for long. She wouldn't separate those concepts either, now; 'all we have is means', as the saying goes.

It was complicated, at UNIT, but she didn't regret staying. Leaked some documents when they were doing something too unconscionable, but she understood the necessity. Defending the Earth… Well, what she thought was necessity.

Acid spreading across the surface of the planet.

Is she the Liz Shaw that would have always chosen to not, is the question. Not work with them, quit everything remotely close to government work if she had to, to make sure information like that wasn't there? PROBE was fine, mostly thanks to Patsy's finagling at the start, but- she had thought UNIT was 'fine' too. That was probably not a word you apply to secret organisations! They're never always-

She crumpled into a hug. 'I did say I trust you. God, Liz… I don't know of any bioweapons anyone's hiding from me.' Her tea was probably cold already. 'And don't say that I wouldn't.'