The landscape was grey rather than white. Even the sun seemed to have dimmed and struggled to spread light on the snow and ice.

Curtis shuffled forwards, his legs heavy and his head leaden. The black mist was returning both inside his mind and outside it. He could feel his consciousness slipping away, his individuality trembling on the brink of the event horizon, about to tumble over. He had to get to the ice cave, had to find the light sources and enter their influence, had to stagger back to the very beginning. It would get easier as he went, it had to as the influence ebbed away.

He could see the hole in the side of the glacier, the opening made by the British soldiers earlier. He had seen them carrying a large rectangular block of ice up the slopes to the Inst.i.tute. Curtis had been tempted to make a detour, to absorb them and try to eke out a few more minutes of humanity. But he could sense that the time was gone. He had drawn out his own life as far as he possibly could in that manner.

So many deaths.

It had to stop.

Holiday was right. Holiday was always right. Ever since he had stopped Curtis as he left the television studio, so many years ago. Before he even knew, when he thought it was just an ability a talent he could control. Everyone had thought he had to concentrate, to exert his mental energies to make things fall towards him. But Holiday had understood at once. He knew, knew the increasing effort Curtis had to go to just to stop things falling towards him.

Trying to sleep was the worst, sleeping while keeping his affliction in check. And the dreams. Such dreams.

But it was nearly over now. He was in the cave. He could see the ice formation, just as Holiday had described it. The image of the man frozen in the ice frozen in time was etched into the ice.

He made his foggy way across the cave, arms outstretched, his eyes black pearls within the dark mist that grew over his face, his neck, his shoulders...

'Over a century?' Fitz shivered. 'You're kidding.' He was clutching a mug of hot coffee and wrapped in a thermal blanket. 'A day maybe. And believe me, that was long enough.' Since the Doctor was absorbed in his work on the watch, Fitz turned to Anji for rea.s.surance. 'I don't look a hundred and fifty or so, do I?'

'You look bad,' she said. 'But not that bad.' She was struggling to resist the urge to hug him. Again. If he hadn't been shivering so much, she might never have let go of him the first time, after he staggered out of the broken ice. 'Pity we've only got about five minutes left before we get blown up.'

Fitz shrugged as if this was nothing out of the ordinary. 'And what's with you, George?' he asked. 'I know I said I'd seen through you, but...' his tone was jovial, but Anji could see there was a hard edge to his words. Some unspoken disagreement that reached into Fitz's eyes, and made George shuffle uncomfortably.

'Fitz,' he said hesitantly, 'I... I don't know what to say. This is... good.' He shrugged. Anji thought that maybe he wanted to hug Fitz as well. But he couldn't his Victorian principles wouldn't allow it any more than his nebulous form could actually do it.

'No, it isn't good.' The Doctor was pacing up and down in front of them staring at the watch. 'Not good at all.'

'Well, thanks for that,' Fitz said.

'There must be a way to stop this thing. What was that?' The Doctor paused. 'Oh, it's good to have you back, Fitz. But what it tells us about the state of the universe isn't so good.'

'If this Curtis guy is so dangerous why don't we follow him and take him out?' Nesbitt asked.

'Take him out?' The Doctor seemed perplexed. 'He's turning into a black hole and you want to, what, buy him dinner? Discuss it over canapes?'

'I meant kill him,' Nesbitt said.

'How do you kill a black hole? How do you defuse an elemental time bomb that's about to negate the universe?'

'There must be a way,' Anji said, pleaded.

'Yes, there must,' the Doctor agreed. 'But we'll find it by thinking, by using our brains. Not by charging around shooting at people.'

'I imagine,' Sabbath said quietly, 'that Mr Curtis has reached the ice cave by now. We should see some interesting effects before long I fancy.'

'I don't know what you're so smug about,' Anji told him angrily 'You'll get blown up too in couple of minutes.'

Sabbath smiled at her. 'I have absolute faith in the Doctor's abilities. If not his mental reasoning and grasp of temporal theory. I'm about be proved right, and the Doctor proved wrong. So there you have several good reasons.'

'Er,' said Fitz, 'look what exactly is happening? I mean apart the end of the universe thing, obviously.' He was staring at MacMillan, apparently fascinated by the sight of the young woman old lady's clothes. She smiled back at him and shrugged.

Anji looked away, annoyed.

The Doctor sighed. 'It doesn't matter. For the most part. But Maxwell Curtis is changing. Rapidly changing. His transformed nature warping s.p.a.ce*time. He's so heavy now heavy in temporal as well physical terms that is that time is bending round him.'

'Is that possible?'

'You didn't see what happened to the floors and ceilings when he was in here,' Anji told Fitz.

'And time as well?'

'Look.' The Doctor swung one of the chairs round and sat on it backwards. His arms were across the back of the chair as he explained, 'Imagine that the layers of time are like sheets of thin rubber stretched tight.' As he gestured he seemed to realise that Hartford's watch was in the way.

'If you say so,' Nesbitt said.

'I do.' The Doctor held out the watch. 'Any chance one of your people can sort this out in the next', he paused to check the countdown, 'minute and a half?'

'Lansing,' Nesbitt said, handing the watch to him.

'Now,' the Doctor went on, 'there are tiny gaps between every second, every minute, every year. Interstices in time, if you like. But in the present time, on the sheet of rubber that represents "now", Curtis is such a focal point for the temporal and gravitic waves, that it's like he's a heavy stone a pebble of compressed matter placed on one of the sheets.' The Doctor smiled thinly. 'OK?'

Evidently he considered the explanations over. He stood up and started pacing again.

'So what does that mean, exactly, Doctor?' It was Nesbitt who asked.

The Doctor sighed, and sat down again, angling his chair so he could address everyone equally. 'That sheet, the "now*sheet", then bends downwards, until it actually touches the sheet below. And in turn, that next sheet is forced down On to the one below that, and the next and the next... Ad infinitum. Time is literally overlapping, intersecting with itself.'

He stood up again, and kicked one of the melting shards of ice across the room. It tinkled into a corner. 'The TARDIS has a special affinity with time. As, I suspect, does the light in the ice cave. Which gives us proof of the hypothesis. A shadow of the TARDIS pa.s.sing back through time in the form of the ice*TARDIS.'

'And how come I was inside it, then?' Fitz wanted to know.

'I think you survived because neither Anji nor I would admit you were definitely dead.'

'Thanks. I mean that, actually.'

The Doctor grinned suddenly, and punched him lightly on the shoulder. The sleeve of his jacket slipped down from the torn shoulder as he did so.

'Still not got it mended then?' Fitz asked him. 'I can recommend a good tailor, if you need one.'

'No you can't,' Anji told him.

'You're another indeterminacy,. Fitz,' the Doctor said. 'Another one that needed to be resolved. Like George here.'

'Oh?' George asked.

'Yes, the real you is still frozen inside the ice. What you are here is a might*be, a possible*George. One that can interact with us up to a point, but which hasn't yet solidified into true reality. And maybe you never will,' he added quietly.

'You've lost, Doctor,' Sabbath said. 'Why don't you just admit it?'

'And let reality unravel like...' He struggled to think of a suitable simile, pulling his ripped sleeve back up into place as he blew out a long breath. Then he frowned. The Doctor's forehead creased for a moment in concentration. He turned to face Fitz. 'What do you mean, "a good tailor"?' he demanded.

George laughed. 'He means you haven't mended your jacket since we met in St Petersburg.'

The Doctor grinned back. 'Of course.' He shook his head as if wondering how he could have been so stupid. But when he looked again at Fitz, Anji could see that his expression was serious. 'Tell me about St Petersburg,' he said.

The light shone in and around him. It was dazzling and illuminating. Through it he could see a tunnel light like ice sloping gently downwards. He started walking.

Walking now.

Walking a minute ago...

An hour ago...

Last year...

Towards Time Zero.

2: Paradox

Sabbath made to stand up, but Nesbitt pushed him back down into his chair.

Lansing stepped forward, holding the watch carefully in the palm of his hand. 'I haven't a clue about this, sorry.' His expression and his voice were grave.

00:27.

00:26.

00:25.

'Let's hope we've found all the charges,' Nesbitt said.

The Doctor lifted the watch from Lansing's outstretched hand and tuned it over. 'Yes, let's hope so,' he agreed. 'But in case you haven't, I'll just pull out this red wire and see what happens.'

'Er,' said Anji.

'Is that safe? Do you think?' Fitz hazarded.

Trix swallowed.

'Oh I think so,' the Doctor said. 'Probably.' And pulled at the tiny wire. It didn't move, and he frowned. 'Tweezers, anyone?'

There was silence.

00:17.

00:16.

00:15.

The Doctor peered closely at the inside of the watch. Then he put it to his mouth and bit heavily at the thin red loop of wire. His face creased with the effort and they could all see the numbers clearly between his fingers.

00:12.

00:11.

00:10.

The wire came free. The numbers froze on 00:08, blinking. The Doctor pushed at his teeth with his thumb as if worried one of them might have come loose.

'Why don't you give up this charade?' Sabbath said. 'There's no way you can win.'

'It isn't a game,' the Doctor shot back.

'We could cheat if it was,' Fitz said in a sulky voice.

'That wouldn't be very fair,' George told him.

'Oh but Sabbath here has done nothing but cheat,' the Doctor said 'Right from the start.'

'How?' Anji asked.

The Doctor shrugged, as if it were obvious. 'He adjusted the time envelope so it will stretch back before it was created. He faked the expedition journal to lead Curtis to the ice cave in the first place. In fact, his whole plan is full of paradoxes and contradictions, isn't it?' He paused again, lost for a moment in his thoughts. 'Well done, Fitz,' he said at last.

'What did I do?'

'Yes,' Anji said, 'how come he gets all the fuss and praise suddenly?'

'It's called charisma,' Fitz told her with a wink.

'It's called something,' she agreed, trying not to glance at Trix as she said it.

'It's called cheating,' the Doctor said. 'The key is in the contradictions. The indeterminates. The unresolved paradoxes. Because,' he said, swinging round to address Sabbath, a note of triumph in his Voice, 'the universe works the way I say it does, not the way you a.s.sume. If the TARDIS really did split reality, nothing I did would ever have any meaning or consequence. There would be no point.'

'And that bothers you?' Sabbath asked.

'It would if I thought for one fraction of a moment that it was true, yes. But it isn't.' He leaned close, reaching over Sabbath's shoulder and holding the back of his chair. 'And I can prove it,' he said. 'Come along!' He moved so fast that he was a blur. Galvanised suddenly into action, running at full tilt from the Great Hall.

'Where's he off to?' Nesbitt asked.