The Doctor stopped her with a touch on her arm. 'By the way,' he said, 'apology accepted.'

'What?'

'For very nearly blowing us all sky high. You did say sorry when you first found us, but I was a little busy at the time.' He flashed a smile.

'Not to mention slightly deaf.'

Stoker let the tension go, her shoulders visibly sagging.

'It's OK. Let's forget all about it. Sorry for snapping like that back there, but...' she let the sentence hang, finishing it in her head.' I'm a little jumpy right now. I'm a little jumpy right now.

He was looking at her again in that way, slightly guileless, but somehow sharp as a laser. 'But?' he prompted, unwilling to let it drop.

Stoker took a breath. 'It's just this place, I suppose,' she replied, waving a hand at the glossy green rock surrounding them. 'It's pretty grim down here.'

The Doctor nodded, frowning slightly as he stuck his hands into his pockets. 'Yes. It's pretty grim on the surface too, I seem to recall...'

The TARDIS had materialised in the shade of an enormous outcrop of rock, some forty feet high and half as wide. The jagged stone surface was the colour of putrescent meat, coated with some kind of mould or lichen. Nyssa was examining the growth minutely, and Tegan thought she must have been-trying to conceal her anxiety with calm, scientific interest in her new surroundings.

'The whole moon appears to be covered in this lichen,'

Nyssa observed. 'I suppose something must account for its atmosphere.' The air was thin but breathable, and uncomfortably cool. Watching her breath steam in the air, Tegan said, 'No other sign of life, at any rate.'

'And yet...' Nyssa sounded troubled.

'What?'

'I have the distinct feeling we're being watched.'

Automatically, they looked skyward. Looking down on them like a giant, bloodshot eye was the planet, a bloated ma.s.s of churning scarlet and black. It was both strangely compelling and utterly repellent. The scabrous colours swirled across the surface in volcanic torment, and it looked to Tegan as though nothing natural or good could exist there.

Repulsed, she looked away.

The Doctor stood some distance from the TARDIS, hands in trouser pockets, Panama hat perched on his head, for all the world looking like someone expecting to attend a garden regatta. His white trainers had left a track of footprints in the crusty sand.

'Feeling better?' Tegan asked him, folding her arms. It was definitely a bit chilly 'I suffered a tremendous psychic blast, Tegan,' he said without looking at her. The eyes beneath the brim of his hat were fixed on the horizon. It wasn't all that far away; the moon seemed quite small.

The Doctor had come round in the console room pretty quickly, jumping to his feet with unlikely vigour. He'd shrugged off Nyssa's concerns and Tegan's offer of a stiff drink. Instead, after glancing at the stationary time rotor, he had simply unfurled his Panama and flicked the door lever down. Now Tegan was struggling to think of something useful to say. 'Breathe deeply and -'

'And relax, yes, I know.'

'Sorry Just wanted to help, that's all.'

'In that case, tell me what you see. I want to make sure my perceptions haven't been interfered with.

Tegan pulled a face and then examined the scene around her once more. The mould-coloured plain was dotted with huge, thrusting rocks, jagged as knives. The crag the TARDIS had landed next to was one of the smaller ones. It looked as though the whole moon was covered with them.

And it was a smallish moon, right enough: she even fancied she could see the curve of the horizon. And up, beyond that, outer s.p.a.ce.

For a long moment, Tegan simply stared at it, and she noticed the Doctor was doing the same. Even he seemed impressed.

Beyond the blood-red planet, the sky was split in two.

One half was a great wash of colour, blue and purple and burgundy speckled with a million stars. Tegan knew that every star was a distant sun, and for a second she felt a dizzying sense of vertigo as the scale of what she saw hit home. I'm so insignificant, insignificant, she thought. she thought.

She switched her attention to the other half of the sky, which was the complete absence of colour: total blackness.

There were no stars, however distant, just a void of unremitting darkness. She shivered.

'What's out there?' she asked the Doctor. Her breath wisped away on the cold breeze.

'Nothing,' said the Doctor bleakly. 'Well, nothing until you reach the next galaxy. That, Tegan, is intergalactic s.p.a.ce, the empty void separating the galaxies?

'It's awesome. It's so empty it's creepy.'

'Whereas that,' the Doctor gestured to the sparkling luminescence on the other side of the sky, 'is full of life and light and energy. The galaxy that this world belongs to, seen in all its glory'

'And the planet?'

'I doubt there's anything much alive there, but you never know.'

'We must be on the very edge of the star system,'

observed Nyssa as she joined them.

'Yes,' agreed the Doctor. 'The last planet before the void.'

'Why did the TARDIS bring us here?' wondered Tegan.

Nyssa was staring out into the pitch black of empty s.p.a.ce. 'It's like my dream... So cold, and merciless. Abysmal.'

'Oh, I don't know,' said Tegan. 'It's kind of scary and exciting, like reaching the top of a rollercoaster.'

'No,' said the Doctor. 'Nyssa meant what she said.'

abysmal. Bottomless, immeasurable depth. The edge of nothing but primal chaos.' Bottomless, immeasurable depth. The edge of nothing but primal chaos.'

'Can you feel it too?' asked Nyssa, her voice wavering.

She pulled the collar of her jacket tighter.

The Doctor nodded. 'It's here. Somewhere close, waiting.

Impatient.

'What is?' demanded Tegan.

Nyssa said, 'The thing that came to me in the TARDIS.'

'You can both sense it? Now you're giving me the w.i.l.l.i.e.s.

Why don't we just go?'

'There's no point,' said the Doctor. 'It would find us wherever we went'

'What? How?'

It came to me while we were in the s.p.a.ce-time vortex, remember?' explained Nyssa. 'It wouldn't matter where we tried to go, if it can find us in the vortex'

'Right, that's it,' Tegan declared. 'Let's find this thing, whatever it is, and get rid of it.'

But neither the Doctor nor Nyssa seemed to be listening; they were both staring up into the darkness.

And it was then that the ground had exploded beneath their feet.

Chapter Four.

Nyssa woke up suddenly.

Her throat was dry but she was unhurt, apart from a pulsating headache. And a very tender swelling on her forehead. There was some sort of dressing on the wound, but she reasoned that it could not have been that bad an injury if she had actually woken up.

'Take it easy,' said a familiar voice, Gentle hands helped her into a sitting position.

'Tegan,' Nyssa gasped. She felt nauseous. 'What happened?'

'Never mind about that now,' said Tegan. 'Would you like a sip of water?'

'I think I'm going to be sick.'

'Relax, you're all right. It's just a mild concussion.'

'Where's the Doctor?' Nyssa's memory felt cloudy, the events leading up to the explosion a patchy blur. Explosion.

She remembered that well enough. The earth had leapt beneath them, a sudden wrench that hurled them all into the air, tossing them like leaves in an autumn squall. She recalled the noise, a thunderclap, her ears buffeted and instantly silenced. Even now they were ringing.

Then the fall, the long, painful descent through stone and dust and debris, losing contact with the Doctor and Tegan in the choking slide of shattered rock. And just before losing consciousness, Nyssa had seen the sky above them for the briefest moment before it was replaced by the sudden darkness of oblivion.

Tegan said, 'The Doctor's talking to someone called Stoker. She's some kind of archaeologist, got a whole team down here. I think they were using explosives to help dig a tunnel or something.'

'We're underground?'

'Yeah. The explosion blew a hole straight through to the planet's surface, right where we were standing!'

'And we fell through the hole?'

'That's about the size of it, yes'

'Then we're lucky to be alive.' Nyssa eased her legs gently off the bed. The material of her trousers was covered in rock dust, and she patted it without much effect. 'Where are we, exactly?'

'We're on a moon that orbits the planet Akoshemon.

Stoker's lot are hoping to dig up the remains of some ancient alien civilisation, apparently. They sort of dug us out of the rubble first, though.'

In the main cavern, Stoker was attending to a minor dispute between two of her men concerning faulty equipment. For the moment she seemed to have forgotten about the Doctor, and so he took the opportunity to strike up a conversation with Bunny Cheung and Vega Jaal.

'Did you say your sponsor was the University of Tyr?'

Bunny nodded. 'That's right. Stoker received a grant from the Department of Alien Antiquities. They've quite an interest in this region of s.p.a.ce. If Stoker finds what they're looking for, she'll be well rewarded.'

And you?'

'Percentage of the profits'

'Excuse me a moment.' said the Doctor, squatting down.

He picked up a fragment of rock from the cave floor and examined it in the light of the nearest lamp. He showed it to Vega Jaal. 'What do you make of that?'

'Porizium; said the Vegan instantly.

'Are you sure?'

'I'd recognise it anywhere.'