Sam hesitated. Then she looked the Doctor in the eye, and said, 'Eight-point-five.'

The Doctor jumped back as if she'd hit him. 'What?'

Sam broke away from him and hurried along the street after Kitig and Narunil. She wanted to explain about the Jones-Richter scale, but she was trying to hold in a fit of giggles. She knew the situation was serious, but then, it always was. And she was sure the Doctor was overreacting. This place was so peaceful, so good good. It might not be the world they'd left behind, but it could hardly be a threat to the existence of everything.

And anyway, Sam didn't like being told off for no good reason.

After a moment the Doctor came up behind her and put a hand on her shoulder. 'I'm sorry, Sam.'

She finally had to let the giggles go. 'And so you should be,' she spluttered. 'Browbeating me like that. The Tractites are hardly Zygons, are they? Or those stupid Daleks you go on about.'

The Doctor stared at her in amazement. 'But I didn't know what you were going to say next! I had to make you realise '

'Realise what? That we're stranded in a dodgy situation again? Come on, Doctor! I can work that out for myself, can't I?

Do you have to tell me everything? I'm not stupid, you know!'

The Doctor turned away without a word and began staring into one of the buildings. The window showed that it was full of water inside, blue water with bright corals and thousands of small, brilliantly coloured fish.

Sam stepped towards it, saw the Doctor's face reflected in the dark water. It seemed disembodied, timeless no, not timeless. Old. Sam remembered his jokes about the centuries, his nine-hundred-year diary, and realised that it wasn't all a joke, not always. Inside the youthful energy, the brilliance, was someone who had seen perhaps too many things.

'We all have to be Daleks sometimes,' he muttered, looking down at his mud-caked shoes. 'It's just a matter of knowing when you really don't have any choice.'

Before Sam could even begin to work out what this meant, he looked up again and smiled brilliantly at her, all traces of age and weariness gone. 'Come on, there's a whole world to explore!'

Sam looked ahead and saw that Narunil and Kitig were standing under a glass archway that crossed the street, their heads on each other's shoulder, their arms entwined.

Tractite love.

Not just a world to explore, thought Sam. A universe. A whole other other universe. universe.

Suddenly something that the Doctor had said while he was telling her off came back to her mind.

find out when things changed, and how, and change them back Which means that we have to change something in the past so that this universe ceases to exist Oh.

Sam closed her eyes. Suddenly she couldn't look at the Tractite city, couldn't look at the Tractites who had welcomed them so kindly, so calmly, the Tractites who seemed so totally devoid of suspicion or malice.

No wonder the Doctor had been angry with her for telling them about the alternative universe. Effectively, she'd been telling them, We're going to have to destroy you We're going to have to destroy you.

She could only hope that they hadn't understood the implications.

She made herself open her eyes, found herself looking at the aquarium. She remembered Narunil saying that this was only a small city which meant that there were many more. She imagined them, growing everywhere on Earth, illuminated in their soft colours like the fish in their tank.

She imagined chucking a brick through the glass wall in front of her. All the water pouring out, all the bright fish stranded and flopping on the stone path. Struggling. Asphyxiating.

OK, dying.

We're going to have to kill to kill the Tractites, she thought. Me and the Doctor. the Tractites, she thought. Me and the Doctor.

Kill all of them.

She looked for the Doctor, saw him with Kitig and Narunil, talking. She opened her mouth to call him, but then thought better of it.

Because he was right. There really wasn't anything you could say.

CHAPTER 5.

'Wine's bad for your liver, you know.'

Rowenna grinned at Julie. 'So are candy bars.'

'I ate a slice of pizza first!'

'Case proven.'

The two women were sitting on the floor in their room, ignoring the ancient, uncomfortable beds and the even more ancient and uncomfortable chairs. Above them, insects crawled over the dirty plastic surface of the roof light. Stray bugs flew around the room, occasionally settling on their arms and faces. Propped up against a suitcase, free of her wheelchair, Rowenna felt almost normal, almost as if she could just get up and walk around the room. A few months ago, when she'd been particularly drunk and angry and bitter, she'd actually tried something like that, and paid for the experiment with a night of agonising pain and three days in bed.

Tonight, she wasn't particularly angry and bitter, but she was planning to get drunk.

'That skull,' said Julie suddenly, 'd'you reckon it was a Homo sap Homo sap? I mean, it looked looked like a like a Homo sap Homo sap there wasn't a trace of any occipital ridge. But it doesn't make sense.' there wasn't a trace of any occipital ridge. But it doesn't make sense.'

Rowenna took a sip of her pink wine and thought about it. The skull had definitely seemed too big for any known early hominid. But according to existing theory Homo sapiens Homo sapiens, modern humans, hadn't evolved until half a million years ago.

Julie was right: it didn't make sense.

'Are we sure about the stratigraphy here?' she asked Julie. 'I mean, the sediments are two million years old, right? No one's made some kind of error here?'

Julie shrugged. 'Maybe. But it's unlikely.' She took a bite of her Snickers Giant Size, went on in a muffled tone, 'Hell, Rowenna, people have been digging in the Kilgai for thirty years. Any anomalous strata would have shown up by now.'

'Perhaps it eroded out,' Rowenna suggested. 'Or fell down from a higher level. Or got washed down when the river flooded in season.' But even as she said it, Rowenna knew that it was unlikely anything so delicate as the skull they'd seen would survive such a process even partially intact. Even the fragment Julie had found would probably have been ground into smaller, more eroded pieces by processes like that.

Julie reached across for the wine, took a swig straight from the bottle. 'If that goddamn soldier boy had let us near the skull we wouldn't have to guess at it like this. We'd be looking at it now.'

'I know,' said Rowenna quietly. 'If I could walk I reckon I'd go out there first thing in the morning, military restrictions or no, and just hope that Captain Jacob Hynes and his friends didn't see us.'

'Well, I reckon I'm going to make that complaint. Perhaps if we put a rocket under his ass he'll let us in.' Julie stood up, wavered across the room towards a cluttered table, in the middle of which sat a palmtop computer. ' "A murder of crows, a military of idiots",' she muttered, tapping away at the keys. LEDs winked on the external modem linking it to the satphone they'd set up outside. 'What's the goddamn e-mail address for this United Nations Intelligence force?' she asked after a while. 'I can't find it anywhere on the net.'

'How would I know a thing like that?'

'Didn't you know someone in England who worked for UN Intelligence?'

It took a moment for Rowenna's alcohol-fuzzed brain to work out who Julie was talking about. When she did, memories flooded back: the cottage on the green hillside in Wales, the protest marches with Cliff and Jo, the older woman's hair flying like a banner in the sun. It had felt wonderful then, it had felt like the world was going to change.

Well, it had, but not in the way she'd expected.

Hell, she'd been so young young then. then.

And so dumb.

'You know, the one who reckoned she could "time travel".' Julie fluttered her fingers at the end of the sentence as she adopted what she felt to be a suitably spooky tone.

Her voice brought Rowenna back to the present. She looked into her wineglass, hesitated. 'I never really believed that stuff.'

'Still, it's a lead. I think we should try it.'

'Get my organiser out of my bag, then. I'll have a look for her number.'

Rowenna looked out of the dirty plastic window of the lab at the dusty, lamplit forecourt. Moths and beetles flickered around the lights, and the ghostly smudge of the moon was visible above the rocks. Julie was out for a walk, too restless to sleep. She'd taken the satphone handset, said something about calling Jo, trying to get an authorisation through before morning.

Rowenna knew how she felt. She couldn't stop thinking about their find.

The impossible skull fragment. The impossibly ancient 'modern' human.

The faint rattle of the disk drive operating on Julie's computer made Rowenna look up. She rolled the wheelchair the short distance from the window to the desk. As she approached, the computer's small screen was filling with the ghostly shape of a fossil skull.

For a moment it was superimposed on the faint reflection of Rowenna's own face, caught in the glare from the overhead light. Her eyes stared back from the empty sockets, her short, neat blonde hair obscured the cranium, and, more bizarrely, the bright-red collar of her sweatshirt was visible around the jaw bone.

Then the colours came up, and the measurements, and a message: ANIMATRIX: Kilgai fragment 1c/45, 6.5.97.

Modeling now complete.

A toolbar offered various options for further work.

Rowenna looked at the image of the skull critically. The program she was using took the measurements of the fragment and built up an image of the most likely complete skull. The computer's guesswork wasn't inherently any more reliable than hers or Julie's, but its results were easier to see.

The complete skull was undoubtedly human. There were no eyebrow ridges, no occipital crest. The jaw was modern, lightweight, and did not protrude. On the other hand, these features were the sorts of assumptions the machine was told to make if the skull was thin, and had a certain curvature. It didn't necessarily rule out the possibility that the fragment was part of the skull of some variant of Homo habilis Homo habilis which just happened to have a thin skull with an odd curvature. which just happened to have a thin skull with an odd curvature.

Rowenna told the computer to add the rest of the guesswork: musculature, cartilage, skin. The process was faster than generating the initial skull map: within a minute, a sketch of a human face was looking out at her.

A completely modern modern human face. human face.

She shivered. To hell with odd curvature. There was something wrong wrong about this. about this.

She found her wineglass on the desk, took a last gulp of the now-warm liquid. Time for bed: perhaps in the morning she'd be able to work out some kind of answer. She rolled the chair away from the desk, towards the door that led to the tiny bathroom. The facilities inside were cramped, and weren't exactly set up for wheelchair users, but Julie had rigged up a rope handle so that Rowenna could manage. She didn't bother with the effort of washing and changing in the cramped space: that could wait until morning.

Afterwards she hauled herself back into the chair, rolled it forward. But at the door she stopped, with her hand on the cold metal of the handle.

She could hear footsteps, moving away.

Very soft, but definitely footsteps. A rattling sound, like leaves, and a faint click. Off to the left? It was difficult to tell, through the door.

Silence. Gone now.

Rowenna hadn't heard the person approach. He or she must have been standing there, must have heard her moving around, heard the faint whine of the chair's motor, and crept away, quietly. Hoping Rowenna wouldn't hear.

She felt her heart freeze for a second, a cold, hard, absolute terror, because all this had happened before all this had happened before.

The board creaking outside the door. The bedroom door, and getting up, half asleep. It must be the neighbour's cat got in again, but no, the intruder in the corridor, no this can't be happening no this can't be happening, a man, a man turning, turning, the gun in his hand, the turning, turning, the gun in his hand, the gun gun Rowenna clenched her right hand into a fist, hard, until the nails bit painfully into her palm.

'Julie?' she called, softly.

There was no response.

Probably some small-time local crook, she thought. Perhaps they think there's something worth stealing here.

'Whoever you are just get out,' she said, trying to hide the panic in her voice. 'Just go. There's no money here.'

A scrabbling, the sound of something being dropped on the floor.

The laptop. Of course. Damn Damn. Computers were worth money anywhere.

She took a breath. 'Look, I'm not going to hurt you, but I need that computer. If you leave it here I'll ' She stopped, aware that her voice was shaking. 'We'll get some money and pay you to leave us alone.'

Silence.

More scrabbling sounds. Hell, the guy was just carrying right on with looking for things to steal. Did he know she was in a wheelchair? Did he think he could just ignore her?

A muttered curse from the other room. More things clattered to the floor.

Hell, if he broke that skull fragment The skull fragment.

There was no way she was losing that. She opened the door, and even as part of her mind was shouting, this is insane, this is insane, this is just what you did last time and got yourself in a wheelchair for life this is just what you did last time and got yourself in a wheelchair for life, she was rolling the chair into the room, into the bright light where a man was sorting through a pile of stuff on the floor.

Not a local. A man in a uniform uniform.

Jacob Hynes.

'What the hell ' she began.

Then she saw what was outside the window.