Sabbath was amused rather than angered by the comment. 'Really, Doctor?' He raised an eyebrow. 'I didn't expect you to have any trouble understanding how something can be bigger inside than it appears from without.' He was smiling now. 'You will be interested to know that it also has very large pockets.' And suddenly he was holding a pistol, pointing it at the Doctor's chest.

The gun moved steadily, slowly, across from left to right. 'Which side first, I wonder?' Sabbath breathed. 'So many decisions. And each time the universe splits. Not a very neat or satisfactory way to go about things.'

'That's hardly reason enough to try to change it,' the Doctor said calmly, 'I a.s.sume that's what you think you're up to here. Collapsing the multiverse back down to a single, manageable, controllable time line. Getting rid of all those unwanted universes that exist parallel to our own. Unwanted by you and whoever it is you keep hinting is pandering to your ego, that is. Letting Schrodinger's cat out of the bag.'

'Despite your unwarranted jibes and insults, Doctor, Curtis will will travel back to Time Zero.' travel back to Time Zero.'

'It might be a bracing walk, but it won't cure him.'

'No, it won't. The energy of the black hole that he is becoming will be released before the universe was even created. All bets are off from that point. The energy spills forwards through time.' Sabbath smiled. 'Who knows, maybe it even kick*starts the Big Bang. But whatever happens, there is a single time line, a single universe that stems from that monumental decision, that one defining event.'

'No there isn't,' the Doctor said. He shook his head sadly: 'The energy means that Time Zero is in effect extended up till now the point where Curtis enters the time envelope. It might wipe out establish history to this point in every universe starting from the single universe that the multiverse sprang from. It might even suppress the universe's own ability to spin off new universes in eleven*dimensional s.p.a.ce. Braynes and strings and super*gravitational waves,' he murmured. 'All very impressive. All very academic. All very impossible.'

'And why is that?'

The Doctor gave a great sigh. 'Because it can't work, that's why. All that will happen if "all" is the right word is that Curtis will become a black hole and suck us all over the event horizon.' The Doctor pushed the pistol to one side, but Sabbath moved it back so it was still pointing at the Doctor.

'He can't travel back more than a hundred years,' the Doctor went on, looking down at the gun. 'He might might might be able to get into the time envelope where George is trapped, but he can't push it back to be able to get into the time envelope where George is trapped, but he can't push it back to before before it was created. He can only travel backwards and forwards within that envelope. To the present, and back to the point where George was trapped.' His eyes narrowed and he leaned forwards, ignoring the gun now pressed into his chest. 'And that is it.' it was created. He can only travel backwards and forwards within that envelope. To the present, and back to the point where George was trapped.' His eyes narrowed and he leaned forwards, ignoring the gun now pressed into his chest. 'And that is it.'

But Sabbath seemed unfl.u.s.tered. 'Is it, Doctor?' he asked. 'Is it really?'

The Doctor shrugged. 'Unhappily, since we're all going to be blown up in', he paused to check Hartford's watch, 'just over eighteen minutes, I'm afraid I won't be here to say "I told you so."'

'Couldn't he use some of his technology from the Jonah Jonah to stretch the envelope?' Anji wondered. The Doctor seemed confident enough, but Sabbath's calm denial worried her, and who knew what sort of equipment he had on board his time ship. to stretch the envelope?' Anji wondered. The Doctor seemed confident enough, but Sabbath's calm denial worried her, and who knew what sort of equipment he had on board his time ship.

'You need some pretty sophisticated time corridor*type technology. Not a vortex Ship. You don't get older or younger as you travel back and forth in the Jonah Jonah any more than we do in the TARDIS. I destroyed the time machine that might have done the trick, though I didn't realise; you wanted it for yourself back in the nineteenth century,' he said to Sabbath. 'That must have been rather galling. And now you discover that the slow light in the ice cave won't work for you either. You have my sympathy.' any more than we do in the TARDIS. I destroyed the time machine that might have done the trick, though I didn't realise; you wanted it for yourself back in the nineteenth century,' he said to Sabbath. 'That must have been rather galling. And now you discover that the slow light in the ice cave won't work for you either. You have my sympathy.'

'No I don't. And anyway,' Sabbath said softly, 'when Curtis tested the time envelope earlier, he travelled back to before before George Williamson was caught in the field. He killed one of your colleagues here in this very castle,' he said to George. 'Isn't that right? He was rather upset about it, came to tell me what he had done.' George Williamson was caught in the field. He killed one of your colleagues here in this very castle,' he said to George. 'Isn't that right? He was rather upset about it, came to tell me what he had done.'

'Caversham,' George said. 'All we found was a black pebble. There was a light, out in the corridor. Then he was gone. Vanished.'

'The opening of the envelope, some of the slow light spilling out into reality,' Sabbath said.

The Doctor was worried, Anji could see. But he did his best not to show it. 'How long before you were buried in the ice was that?'

'The night before.'

'A few hours then.' He breathed a noticeable sigh of relief. 'Well, if that's the best you can do with whatever technology you've acquired, I really don't think we need to worry.'

'Er, Doctor?'

'Yes, George?'

George swallowed. 'I have tried to follow what you are saying. I think you are maintaining that this dimension, this corridor of time that I can walk along does not cannot extend back to much before the moment I found myself trapped within it. Is that right?'

'Yes George. That's right.'

George hesitated. Anji could see him considering whether he should go on. 'But,' he said at last, 'I have walked back and seen the dinosaurs.'

'What?' The Doctor's face was an icy white.

'I watched them on the plains feeding, hunting, living and breathing.' He was staring off into the distance as he remembered. 'It was such a sight.'

'You could have changed history,' the Doctor said, his voice a mixture of anger and frustration. 'Just by being there, without knowing what you were doing, you could have altered evolution even.' He frowned suddenly. 'I wonder,' he murmured, 'if that is why the window, the portal... Why the fabric of reality between these two universes is far more serious than I ever dared to believe,' he said. His eyes were burnt with anger. 'What have you done?'

'Sixty million years or more,' Sabbath said quietly. 'Time Zero approaches.'

'If you're right, it's only a matter of time minutes at the most before we see the whole of s.p.a.ce*time start to fold in on itself. Before the past and the present, this universe and the next become blurred and indistinct. Before everything ends.'

Sabbath raised the gun, his head c.o.c.ked amused to one side. 'Begins, surely, Doctor?'

'Doctor!' The shout came from the doorway.

Sabbath turned, bringing the gun round.

But there was n.o.body there.

The figure that had stood framed in the doorway an instant before was already diving to one side, rolling, coming up again into a kneeling crouch. Rifle levelled and aimed.

The gun leaped from Sabbath's palm as the shot cracked round the room. He cried out and stared down at his bloodied hand.

'Don't move,' Captain Nesbitt told him as he stood up, keeping the rifle aimed at Sabbath.

Without a word, the Doctor handed Sabbath a handkerchief.

'Now then Doctor,' Nesbitt said, 'where would you like us to put this?' He gestured back to the doorway.

Where four of the SAS men were struggling to carry something into the room.

It was the gla.s.sy form of the ice*TARDIS from the cavern.

4: Opening the Dox

'Time travel always splits the universe,' Sabbath said as the soldiers put the ice*TARDIS down in front of the Doctor. 'It has to. One universe where the time traveller is not there, one where he is. Even before the different decisions and events that follow.'

'You think so?' The Doctor gestured for them to put down the ice*TARDIS. 'That's good,' he said to Nesbitt and his men. 'Thank you. By the way,' he went on, 'the late Colonel Hartford left us some presents.'

Nesbitt nodded. 'We found a few plasma*thermite charges. I've got men making them safe now.'

'Good.'

'You don't know how many there are, do you?' Nesbitt asked. 'Only I'd hate to miss even one.'

'A problem?'

'Big problem. Also, we have no idea how long there is till they're set to detonate.'

The Doctor held up Hartford's watch for them to see.

12:33.

12:32.

12:31.

'Not long enough to search the place for other charges, though I've got men on it,' Nesbitt said. 'And we're already too late to get far enough away to be sure of being safe.'

'Great,' Anji said. 'So now the question is only whether we get blown to bits before the universe ends.'

The Doctor was frowning. He had the back off the watch again. 'In theory I can stop the timer,' he said. 'Just one more little thing to worry about.'

Sabbath gave a short laugh. 'That's the trouble with your meddling, Doctor. For all your good intentions you simply muddy the waters. Every problem you solve, every person you save, adds to the complexity and confusion and chaos that is the multiverse. What it comes down to is this: You have no idea what you are doing.'

The Doctor spun round, the watch forgotten for a moment. 'How dare you?!' He was shaking with raw and violent anger. 'You say I don't understand, after what you have tried to do? You think you can restore order to the multiverse, is that it?'

Sabbath inspected his right hand. The bleeding where the bullet had grazed it seemed to have stopped. He dabbed at it again with the Doctor's handkerchief. 'The fact that there exists a window between this reality and the next suggests a connection, wouldn't you say? Suggests that the two can be smashed together.' He held out the bloodstained handkerchief.

'Smashed being the operative word.' The Doctor s.n.a.t.c.hed his handkerchief back and stuffed it into his pocket. 'You travel through the vortex in your aptly*named Jonah Jonah, and you don't even understand the basics of temporal mechanics, do you?' He shook his head annoyance and returned his attention to the inside of the watch.

Now Sabbath looked disconcerted at the Doctor's vehemence. 'What do you mean?'

'I mean,' the Doctor said without looking up, 'that the universe doesn't work in the way you think it does. You're forgetting the cat. At the very least you're overlooking when that split occurs.'

Sabbath's eyes narrowed. 'Go on.'

'The universe doesn't split when I travel in the TARDIS. It doesn't split when I intervene.' He turned the watch over and thumped heavily on the top of a table several times as he spoke. 'Because I know what I'm doing.'

'Really?' Sabbath folded his arms across his chest. 'And what, pray, does happen, then?'

'That depends. The universe remains in an indeterminate state like Schrodinger's cat. Neither one choice nor the other. Any of a selection of events or decisions may have occurred. It really doesn't matter. Because I travel within a single universe. The real real universe for want of a better term. We don't flit about between them on a whim. That really would be chaotic.' universe for want of a better term. We don't flit about between them on a whim. That really would be chaotic.'

Anji could see the face of the watch as the Doctor continued to jab at its insides: 11:24.

11:23.

11:22.

Sabbath seemed to consider. 'And this indeterminate state...?'

'Is later resolved. At a point in time when it is apparent what has really happened, the whole interlinked set of choices the web of time if you like crystallises along a single path and forms a pattern.' He stepped closer to Sabbath and looked him directly in the eye. 'That's what free will is all about.' His voice was a low husky whisper that barely carried to Anji as she strained to hear him. 'But perhaps that is what your friends, whoever they might be, are really out to suppress.'

Sabbath was silent for a while. The whole room was silent. The soldiers looked at each other, their expressions professionally neutral as they stood patiently by the ice*TARDIS. George looked from Anji to the Doctor and back again. Anji's own attention was fixed on Sabbath.

'It's an interesting theory,' he said at last. 'Though I don't think either of us will be able to prove it one way or the other.'

'Not from the wrong side of an event horizon, I agree.' The Doctor turned to Nesbitt. 'Could I borrow your rifle for a moment?' he asked. 'I'd like to try to prove a theory of mine.'

'My pleasure, Doctor,' The SAS Captain handed the Doctor his a.s.sault rifle, keeping a wary eye on Sabbath. Corporal Lansing moved slightly to cover him from the other side of the table.

For a horrible moment, Anji thought the Doctor had reached the point of such frustration that he was going to shoot a bullet through the watch. But to her relief he stuffed it back into his pocket as he took the gun.

'Let's try a for*instance,' the Doctor said as he weighed the heavy rifle in his hands. He held it by the barrel, pointing the b.u.t.t at the ice*TARDIS.' My TARDIS may or may not arrive in the ice cave in George's time. Perhaps Fitz just imagined it had or hoped it would. And I really don't know if it will or not, but it's possible either way. True?'

'I suppose so,' Sabbath admitted.

'So this shadow of it, this ice*TARDIS if you like, is a manifestation of that indeterminism. It makes apparent the state of "maybe". Yes?'

Sabbath nodded slowly. 'Not that it matters.'

'Oh it matters,' the Doctor said severely. 'The very fact that we can see that manifestation made real before us is indicative of the fact that the whole structure of s.p.a.ce*time, the multiverse itself is collapsing. Just as you planned. It will, is and has happen, happening and happened. All at once, here in this universe, And the effects will spill out and speed up and spiral out of control if we don't stop Curtis soon.'

'But if that's true, Doctor,' Anji said, 'why haven't we seen other signs of it? Before now even. I mean, if it's rippling back or whatever to Big Bang and beyond.'

'Perhaps we have,' the Doctor said grimly. 'Like an image of George walking past the Cold Room, replayed over and over from another time. Or whatever temporal anomaly alerted Hartford's superiors the fact there's a time machine near here... The window between the worlds where reality is stretched so thin a bullet or a rock can pa.s.s through its very fabric.' His voice dropped an octave. 'It has to be stopped,' he said emphatically.

'So what do you suggest?' Sabbath asked, smugly. 'As you say, it is happening already.'

'Not quite. It is still undetermined exactly what will happen. As Schrodinger would tell you, inside the box the cat may or may not be alive. And there's only one way to find out.'

As he said this, the Doctor stepped forwards. Anji flinched as he raised the rifle high above his head and swung it down savagely at the doors of the ice*TARDIS.

The ice*TARDIS exploded like fragile gla.s.s, ice crystals hurled across the room and crashing to the stone floor. The Doctor raised the rifle again. But there was nothing left to swing it at.

Nothing except for the figure that stood silhouetted where the ice*TARDIS had been. The figure that had been standing inside it. The figure now slumping forwards and collapsing to the floor.

Anji's hand was over her mouth, stifling her scream.

The figure struggled to his feet, Wiping a stubbly chin across his sleeve in confusion and blinking at the light. A book dropped from the man's hands a leather*bound notebook. The pages were ragged and some were falling out. It fell face down on the floor and the man stared down at it in confusion and surprise.

'I think this is yours,' the Doctor bent down and picked up the book.

He closed it carefully and pressed it into the figure's trembling hands.

'Thank you, Doctor.' His voice was hoa.r.s.e and dry. But it was as distinctive as his silhouette, as the stubble on his chin.

'Fitz!' Anji gasped.

3: Indetermined