The cube gave an intense, spasmodic surge, showing a capability Turlough hadn't been aware of. He tried to resist the wrenching pain that came with it, but he couldn't prevent himself from crying out.

' Kill the Doctor Kill the Doctor!' the Black Guardian urged, and the agony stayed for several seconds longer. Turlough fought not to cry out again. Tegan might hear and come to see what was happening. If she did, and if his secret was uncovered, he knew what the cube's next order would be.

'I'll do it,' he gasped as the glow died and the pain receded. 'I have a plan.'

' You have nothing. You have nothing. ' '

'I do. But I need to get back to the TARDIS.'

' Why Why?'

'Trust me,' he pleaded, knowing that he had little chance, and it was then that he heard Tegan calling.

She must have heard something. Quickly, he went on, 'How do I recreate the door?'

' Fail me again... Fail me again... ' the Black Guardian said ominously, but Turlough did his best to put a confidence into his voice that he didn't feel. ' the Black Guardian said ominously, but Turlough did his best to put a confidence into his voice that he didn't feel.

'I won't, I promise. But how do I get back?'

' You have skills, use them. Look beneath your feet. You have skills, use them. Look beneath your feet. ' '

Underfoot? What could he have seen under the floor that would give him a clue to the way back to the TARDIS? He tried to think through the stages which had led to the creation of the door: the breakup, the emergency programme set to home in on the distinctive radiation waveform of a pa.s.sing ship...

Tegan was coming around the corner. He realised that he still had the communication cube in his hand, and he quickly pocketed it.

He thought he had an answer.

Tegan was looking puzzled. She'd been expecting to find him in some kind of trouble. 'What are you doing?' she said.

'I need you to help me. We've got to find the place where the door to the TARDIS appeared, and then we've got to find a way of lifting one of the floor panels.'

'But why?'

'I'll explain when we get there.'

The catwalks deep inside the Terminus were considerably different to those that had been added by the Vanir and by their immediate predecessors; these had been built for bodies with dimensions that were decidedly non-human. It wasn't as difficult as the Doctor expected to find the lines that Bor had identified as power and control cables, because his tracks were fresh in the dust. It seemed that the Garm kept to his own areas, and they didn't include anywhere above floor-level.

The lines and cables were colour-coded, and they ran parallel to the walk. Kari couldn't understand why they were following literally in Bor's footsteps at all.

'But what's the point?' she said. 'He's crazy.'

'Crazy to think he could make an effective radiation shield out of junk, yes,' the Doctor conceded. 'But he knew what he was talking about.'

'I wish I did.'

'They're using a leaky containment drive as a kill-or-cure, that's risky enough. If we don't get out of here soon, we'll glow in the dark for the rest of our lives.'

The Doctor was hardly exaggerating. With access to the facilities in the TARDIS, he was confident that he could reverse the effects of mild radiation contamination. It was a fairly simple case of rigging a low-power matter transmitter with a discriminating filter between the two ends. But when the contamination had been around for long enough to cause actual cell damage on a detectable scale, there was no way of reversing the process.

'But you think there's an even bigger danger than that?' Kari said.

'Bor seemed to think so. Follow these lines, and we'll find out why.'

They carried Bor into the Vanir's converted storage tank and laid him on one of the bunks. He was weak, and he was starting to become delirious again after a brief period of lucidity. Someone was sent to get Eirak, and Sigurd crouched by the bunk.

'You hear me, old man?' he said.

Bor stared at the ceiling. 'Sigurd?'

'Why did you do it? You knew you wouldn't last.'

'Worth a try... the pilot's dead, you know.'

'Which pilot?'

'Pilot of the Terminus.'

Now he was definitely rambling. The Terminus hadn't moved under its own power or anything else's for generations. Sigurd said, 'The pilot's dead and long gone.'

'Oh, no,' Bor insisted, 'he's still there. But he's going to fire up the engines, and they won't take it.'

There was a noise from behind. Sigurd looked up to see Eirak on his way over from the door. He came and stood by the bunk, and glanced from one end to the other. 'Where's his helmet?' he said making no attempt to lower his voice.

'He didn't have it.'

Eirak inspected Bor's ruined armour critically. 'Did he say why he went into the zone?'

Sigurd shook his head. 'I can't make sense of it.'

'Well...' Eirak straightened. 'One less on the rosters.'

Seeing that the watch-commander was about to leave without further comment, Sigurd said, 'But he needs Hydromel!'

The answer was harsh and direct. 'There isn't any to spare.'

'But he's dying!'

'So why detain him?' Eirak said curtly, and he walked away.

The Doctor and Kari had followed the control cables to their end; they led to the control chamber of the Terminus ship.

It wasn't easy to get in. The floor and the ceiling had been built on a slope, so there was hardly enough headroom. A recess had been cut into the slope for the central control couch, and all of the controls and displays had been packed into the available s.p.a.ce around this. It didn't leave much s.p.a.ce to move around.

Not that the pilot needed any. He was most definitely dead.

The suited body in the couch was half as big again as a man, its contorted alien face half-hidden by the tinted bubble of a pressure helmet. As the Doctor crouched and moved across for a closer look, he could make out only a few details by the lights of the live instrumentation. They gave the alien the look of the screaming skull design that had been painted on the outside of the Terminus ship's hull.

It seemed all wrong. The place didn't have the feeling of long-ago disaster that he'd been expecting.

Something had gone wrong the dead pilot and the damaged reactor globe down in the engine section were evidence of that but from what he could see around him, the Doctor would have guessed that all of this had happened only hours before. And that, of course, was impossible.

Kari seemed fascinated by the dim vision of horror that could be made out through the alien's visor gla.s.s.

Squeezing himself between units for a closer look at a part of the console, the Doctor said, 'Do you remember Bor telling us that one of the Terminus engines had exploded?'

'Did he?' Kari said, only half-aware.

'Look at this panel.' he pointed, and Kari had to shake herself to concentrate. The Doctor went on, 'The Terminus was once capable of time travel.'

She stared. The layout meant nothing to her. She was combat section. She said, 'So?'

'To push a ship of this size through time would take an enormous amount of energy.'

'What are you getting at?'

'Think about what we've learned. The Terminus seems to be at the centre of the known universe.

Imagine the ship in flight. Suddenly the pilot finds that he has a vast amount of unstable reaction ma.s.s on board. What would you do?'

Kari didn't have to think it over. 'I'd jettison. It's the only answer.'

'And a perfectly normal procedure, under more conventional circ.u.mstances. Unfortunately, this pilot ejected his fuel into a void.'

'And it exploded.'

'Starting a chain reaction which led to Event One.'

It took a moment for Kari to grasp what was being said, but then her eyes widened in amazement. 'The Big Bang?' she said. 'But why wasn't the Terminus destroyed?'

'As Bor said, it was protected. The pilot used a low-power time-hopper to jump the ship forward a few hours, leaving the unstable fuel behind to burn itself out. He obviously thought it would be a localised reaction and no danger to anybody. Unfortunately, the chain reaction just got bigger and bigger... the shockwave must have caught up with him and boosted the ship billions of years into the future.'

'And killed the pilot.'

'As well as damaging a second engine. Which is still active.'

Kari looked again at the pilot, this time with even greater awe. He was more than an alien; he was the last survivor of a universe which he'd destroyed with his error, and his dying moments had been spent looking on the new universe that he'd inadvertently brought into being in its place.

But if the second engine was still active... didn't that mean that the whole process could take place again?

The Doctor was staring at one of the console controls. 'Did you see anything move?' he said. 'I haven't been looking. why?'

'Something's changed, and I'm not sure what.' He seemed to be looking most intently at a T-shaped control handle that was almost within the reach of the pilot's gloved hand. The three-fingered claw lay on the panel, actually touching nothing.

But as they watched, the handle moved a fraction.

'A pre-ignition sequence!' the Doctor said. 'It's already been programmed in!'

'But he couldn't. He's dead!'

'The ship doesn't know that. It'll go ahead anyway.

We've got to try to shut the damaged engine down.'

'But how?'

'Well,' the Doctor said, shifting himself around to reach across the control panel, 'we can start by seeing if we can reset that handle.'

Olvir tried to get ahead of the Garm, but he hadn't counted on the labyrinthine complexity of the Terminus interior. He couldn't effectively make his way alone, and when he tried to retrace his steps the Garm had, of course, moved on. He listened, but the beast made no sound. It was only Nyssa's weak calling of his name that gave him something to follow. He caught up just as Nyssa was being strapped to an upright before the damaged reactor globe of the ship's engines.

He saw Bor's junkheap. More important, he saw the deadly crack that was only partly covered, light streaming though like the gaze of Satan. Nyssa called his name again, and Olvir started forward.

If he hadn't still been wearing Vanir armour, walking into Valgard's staff might have killed him.

Olvir folded, all the breath smacked out of him. He felt as if he'd been rammed in the midsection by a truck. He hit the floor, sack-like and out of control, as the Garm ambled across his lurching field of vision towards the stacked machine parts. Olvir wondered with a detached kind of curiousity what might be coming next. For the moment, he had only the most tenuous contact with his body and his surroundings.

He tried to focus on the Garm, but Valgard got in the way.

'Where are the others?' he demanded, hefting his staff ready for another blow.

'What?' Sensation was returning to Olvir now, and its return was bad news.

'The other spies!' Cheated of prey once, Valgard wasn't going to allow Olvir any advantages. The staff came down towards Olvir's head in a bone-splitting hammer-blow. Olvir ducked, took some of the force on his protected shoulder, and slid up under the rod to grab hold of Valgard. The staff was useless for close-up fighting, and it was here that Olvir would have the edge of youth and strength.

It wasn't the bonus that he'd hoped. Valgard had over-ridden the metering mechanism on the intravenous Hydromel dispenser that was fixed to the chestplate of his armour, and he'd used up all of his reserves in a single shot. For a while, at least, he would feel immortal. Olvir tried some of his best moves, the ones that had won him points in combat training, but Valgard blocked them all. They spun and they circled, and Olvir had little chance to register what the Garm might be doing.

Valgard tried to break free to make a useful distance for his staff, but Olvir wouldn't let him. Olvir tried to bring his burner around for a close shot, but Valgard knocked it to the floor and kicked it away. They swung around again. Olvir could see that the Garm was leaning hard against the side of the junkheap.

The animal bulldozed the sc.r.a.p aside. Radiant light burst through, and Nyssa was directly in its path. She screamed.

Olvir suddenly switched tactics. Instead of pulling away, he launched himself onto Valgard. The Vanir suddenly found that he was trying to hold the combined weight of Olvir and two sets of armour.

Given warning, he might just have managed it. He swayed for several seconds, but he was already beaten.