'I don't see it,' said Roz, peering into the screen.

112.

'Right next to the crater.'

'That's not a crater,' she said. 'That looks like... I don't know what that looks like. The surface is torn up. Another fake?'

'Something more than that,' said the Doctor. 'Trust me, it'll be safe to land there. The sooner the better.'

'Right. I'll go tell Sekeris and then I'll suit up. Meet you in the airlock?'

'Bring Iaomnet.'

Roz let out a long, slow whistle.

'She can watch our backs. Besides, I want her where I can see her.'

'Doctor, that doesn't make any sense.'

His eyes never left the screen. 'Scenario: we leave Iaomnet in the shuttle. She manages to persuade Captain Sekeris of who she really is. He decides it would be a good career move if no one ever found out he'd ferried us. The shuttle quietly lifts off, leaving us stranded.'

'We'll see you in the airlock,' said Roz. 'Fifteen minutes.'

After travelling with the Doctor for a while, Roz had decided there was a switch inside the human brain marked 'That's Too d.a.m.ned Big'. She had felt that switch flip a few times now, in the presence of objects and creatures and minds that were just a bit much to cope with without a cup of tea, a lie down and a long session of philosophical introspection.

The switch in her head was jammed in the on position now.

She was grateful. It allowed her to think about the size of the things around her without having to comprehend it. Medical advice: never stick anything in your ear smaller than your elbow; never stick anything larger in your skull than, say, a continent.

Roz had expected to have to force Iaomnet out of the shuttle at gunpoint, but the double-eye had jumped at the chance to accompany them. 'I thought I was just going to babysit a couple of professors,' she told Roz, as they pulled on their suits. 'I want to know what's going on.'

'I doubt it,' said Roz. 'Just remember, once we're out there, your life depends on us, and ours on you. All right? Try to get the drop on us in a nitrogen-oxygen atmosphere.'

113.

Iaomnet nodded, seriously. 'If it's anything like Iphigenia...'

She looked up as the Doctor came into the airlock. 'Well, you guys are the experts.'

There was a brief tussle as Roz and Iaomnet checked each other's gear, and the Doctor struggled into the old-fashioned s.p.a.cesuit he'd worn on Iphigenia.

They'd followed him on to the surface, Sekeris's voice nervously drifting after them as they headed over the snow and grit.

Now they were standing at the edge of the crater, looking down into it. She had been right no meteor or asteroid had struck the dirty s...o...b..ll to make this mark. This wasn't random.

Something had smashed its way inside.

Iaomnet said, 'Have you ever seen a bear smash its way into a beehive? In a sim, I mean?'

The rock had been gouged out, and then the metallic surface underneath had been gouged out. Imagine an office block the size of a small city, with all the roofs torn off. The edges of the metal shimmered, reminding Roz of fractal displays.

Here and there Roz could see vast tunnels, vanishing into the heart of the comet. Comet. This wasn't a comet.

But she'd deal with that when the switch turned itself off again.

'How old old is this?' Iaomnet breathed. is this?' Iaomnet breathed.

'Ten million years,' said the Doctor. He scrambled over the lip of the rock and started heading towards the nearest tunnel.

Iaomnet said, 'We can't go in there. It's like Iphigenia, it's '

'Don't say it,' said Roz sharply.

'Come along,' said the Doctor.

They walked for an hour. Roz kept watching the sky, wondering when the Carrier would become visible, trying to keep her eyes off the structure.

Iaomnet seemed oddly comfortable with it. 'It was meant to store something,' she said. 'Or carry something. Something big was meant to move around in these tunnels.'

They had almost reached the edge of the great tunnel. Roz tried to estimate its size, but the scale was confusing, improbable.

Perhaps a kilometre across. She thought of missiles, or alien 114 carrier ships, exploding out of their camouflaged home to devastate astonished empires.

They were standing deep inside the 'crater', surrounded by empty rooms. Roz wondered if they were looking at them from on top, beneath or sideways. It depended on how whoever built this thing generated their gravity, she supposed. She had a bizarre vision of office furniture floating out through the missing walls.

The rooms had white walls or floors, startlingly naked, as though rejecting the snow and filth. Or polished to that perfect white smoothness by millions of years of cosmic dust? Why was there anything left at all?

The Doctor walked up to a human-sized rectangular shape near the edge of the tunnel. To her total lack of surprise, he took out a screwdriver from a suit pocket and started to muck about with some bit of machinery or electronics or whatever it was that had once made this colossal thing tick.

'What are you looking for?' Iaomnet was almost giggling. 'The self-destruct b.u.t.ton?'

'The power relay,' said the Doctor. 'Which I've found. It shut down to conserve energy after ten thousand years of disuse. I'm trying to convince it we're here.'

'It? It what?'

'Ah! There!'

With a rumble they could feel through their boots, the door slid open. Roz realized she was looking at an alien lift.

'You're joking,' she said.

'Trust me,' he said. 'According to the relay, the power systems are quite intact. Much of the structure will have been in protective stasis. In we go.'

Iaomnet pulled back. 'What if it shuts off partway down, or something?'

The Doctor didn't look at her, climbing into the lift. It was big enough to hold a small crowd. Or a single, huge creature? 'There isn't time to think about it,' he said. 'You should stay here if you're not sure you want to come.'

Iaomnet got into the lift with him. Her frightened breathing was loud in Roz's ears. She followed them in.

115.

Roz was expecting the Doctor to do some more creative engineering. Instead, he pressed a few b.u.t.tons. The doors hesitated and then closed, and the lift moved slowly down, down into the body of the comet.

Roz counted the minutes. Three. Four. It was obvious the Doctor knew what he was dealing with. She wished she'd argued him into leaving Iaomnet on the shuttle he was probably holding his tongue in front of the double-eye.

The lift began to slow. Roz suddenly realized there was gravity generated by the floor, she a.s.sumed, since the feeling of slowing down was so gentle.

'The lift runs parallel to the tunnel,' said Roz.

'Where are we going, then?' Iaomnet wanted to know. 'What's at the base of the tunnel?'

The lift doors slid open again, revealing a great black s.p.a.ce.

The Doctor cautiously stepped out of the lift, found the outside wall, and evidently the light switch.

The entire tunnel was suddenly alive with spotlights, patches of blue-hot radiance moving around like insects. Picking out the six walls, made out of the smooth white stuff. Picking out recesses and structures in the walls. Sweeping over the immense skeleton crumpled at the bottom.

The Doctor did more things to the controls he'd found. The lights slowed down, expanded, filling the tunnel with an almost even illumination. 'What the cruk is that that?' said Iaomnet.

The creature's bat wings were spread out, collapsed beneath the weight of its body. The fine bones of the wingtips were as thick as a human arm.

'Don't worry,' said the Doctor. 'They're extinct.'

'Are you sure?'

'This one is, anyway,' said Roz.

'Good,' said the Doctor. 'Because to get where we're going, we'll have to walk past it.'

Roz and Iaomnet followed him out on to the floor of the tunnel.

There were huge doors around its base. Looking up, she could see a hexagon filled with stars.

'Is it just me,' said Iaomnet, 'or does it feel like a horror sim in here?'

116.

'Yeah,' said Roz, surprised. 'You're right. Psychic residue?'

'What?'

'Quite probably,' said the Doctor. 'Like a trace of radiation.'

'Radiation?' said Iaomnet. 'After ten million years?'

'Psi powers don't obey the physical laws of the universe,' said the Doctor grimly. 'Imagine the power of this thing when it was freshly dead.'

'It must have been pretty powerful when it was alive,' said Iaomnet. 'Look at the walls.'

Roz looked up, where the intelligence agent was pointing.

There were great claw marks in the metal. She looked at the hooked claws at the end of the thing's hands, imagining it scrabbling at the metal, trying to climb out. They'd trapped it down here.

'That's how the surface was damaged,' said Roz. 'In a battle with these things.'

'Yes,' said the Doctor. 'The Real World Interface of these early models was rather unstable.'

'The what?' said Roz.

'Where are we going?' Iaomnet insisted. 'I mean, this is incredible, but I'd like to know where you're taking us.'

'The console room,' said the Doctor. 'We'll need to find some transport first. It's going to be a long trip.'

Roz stopped near one of the claws. She just stood there, feeling the switch inside her head snap back off and the size of the thing come crashing down on her conscious mind. The size of the comet. Ship. TARDIS.

'Holy s.h.i.t!' she said.

The console room was surprisingly small. Roz wondered how large the crew had been. Thousands, scattered through the ship?

Six people, one for each panel of the hexagonal console? A single pilot?

They'd got here partly by more lifts and partly in a sort of chunky buggy, meant to carry cargo and not pa.s.sengers, judging by the suspension. Roz hoped it was still working for the journey back they must have travelled fifty kilometres through the angular white corridors.

117.

The Doctor had sealed the area and reinstated the atmosphere.

When he was sure it was safe, he pulled off his bulky s.p.a.cesuit and walked around the console in his ordinary clothes and stockinged feet, muttering.

When his head didn't explode, Roz took off her helmet, unsealing it beneath her chin and letting it hang down her back.

After a while Iaomnet took hers off as well.

'Doctor,' said the intelligence agent, 'how can you work this machinery?'

'My people built this,' he said.

'OK,' said Iaomnet, 'I accept that. But I couldn't operate a spinning jenny. How do you know how to operate these controls?'

'Our technology isn't like yours. What's the word I want?

Stagnant springs to mind.' springs to mind.'

'You mean your technology hasn't changed in ten million years? You mean the people who built this are still around still around?'

'They don't venture out very often,' said the Doctor. 'Not these days. And of course the technology has changed. But only in the sense that the old technology has been refined.'

'Miniaturized,' said Roz.