Tegan took hold of the rail and pulled herself to her feet. 'You're weird, Turlough,' she said. 'What a subject to bring up at a time like this.' And she started to ascend.

'We're just going deeper and deeper,' Kari complained. 'What are we looking for?'

'Whatever it is that makes the Terminus special,' the Doctor told her. 'Something that could even cure the Lazar disease.'

They'd really had little choice over their route. The ribbed tunnel that they'd entered hadn't offered them any interesting-looking diversions, and there seemed little point in returning when they knew that a hostile reception was guaranteed. Kari said, 'There's nothing here but radiation.'

The Doctor considered this for a moment. 'You know,' he said, 'you're right.' And he switched on the hand-radio for a brief burst of the wave interference. It was much louder than before. 'And we're getting closer to the source.'

'That doesn't sound too healthy.'

'It isn't. How safe is an engine when it leaks that badly?'

'You couldn't use it. You'd blow yourself away as soon as you tried to open up.'

'So,' the Doctor said, letting his mind run along the speculative rails that events had presented to it, 'why haven't they just dumped the reaction ma.s.s and made the Terminus radiation-free?'

'You think radiation's part of a cure?'

'I think there's even more to it than that,' the Doctor told her. What Kari had suggested seemed, from the evidence, to be reasonable. If the Lazar disease was caused by a virus or a similar organism with a lower radiation tolerance, a non-lethal dose might be enough to clean it out of the victim's system.

Blanket secrecy and social shame would serve to keep this simple solution from becoming common knowledge. Whoever ran the Terminus the 'Terminus Incorporated' referred to in the liner's automated announcements was obviously taking advantage of the old ship's high incidental levels without either knowing or caring how they were caused.

And the possible causes were beginning to worry the Doctor even more than the disease itself. 'We're standing at the centre of the known universe,' he told Kari. 'Now, don't you think that deserves some close consideration?'

But Kari was no longer listening to him. She seemed incredulous.

'I can hear someone singing! singing! ' she said. ' she said.

Handling of the Lazars was conducted according to a plan originally devised by Eirak. Vanir responsibility for the sufferers technically ended at the yellow line when they were handed over to the Garm, but it seemed that the Company's judgement of their success was based on the survival rate as it was calculated somewhere later in the processing. What happened beyond the line was something that they couldn't know, but it was in their own interests to ensure that as many Lazars as possible arrived to face it alive.

Originally this had meant sending the sickest and least able through first. It looked good in theory, but in practice it was a disaster. They slowed up the whole process so much that even those who'd arrived able to walk on their own finally had to be carried to the handover point. Eirak's answer to this had been the Lazar a.s.sessment, where estimates of the advancement of the disease were made and the fittest sped through first. Which was how he came to be looking at Nyssa.

'She's hardly touched,' he said, putting a hand under her chin and tilting her face towards him.

'Well, compared to some of these,' Sigurd agreed.

Other Vanir were moving amongst the Lazars and pinning numbered labels to them. It was all running in an orderly manner, the way that Eirak liked it.

'Take her first, then,' he said, straightening, and Sigurd turned to beckon one of the others over.

'No, wait,' Nyssa said quickly, and Eirak gave her the cool look that he saved for troublemakers. He'd been right, she was hardly touched. The progress of the disease barely seemed to have advanced beyond the initial stages.

He warned her, 'Don't give us a hard time.'

'But others are worse than me.'

'The fittest ones go first,' Eirak said. 'There's some kind of quota going, and most of these corpses won't fill it. So just co-operate and don't mess up our chances.'

He nodded to Sigurd. Two of the Vanir took Nyssa's arms and raised her, protesting, to her feet.

Tegan and Turlough had found the control room.

They stood in the doorway, taking their first look.

'Maybe they were here,' Turlough said, but he didn't sound as if he believed it. Tegan was looking at the two pressure helmets that had been abandoned on the main console.

'Maybe somebody was,' she said.

They moved in to look around. It wasn't as promising as Tegan had hoped. It was one thing to suppose that you'd be able to spot the control that you needed out of all the others, but facing the reality was something else. She wouldn't even know where to start.

Turlough reached over and tried a couple of switches, 'Hey,' Tegan said apprehensively, 'What are you doing?'

'Messing around, unless you've got a better idea.'

'Well, don't. The situation's bad enough.'

'We've got to try things,' Turlough insisted, and to demonstrate he tried a couple more. All of the screens at every crew position suddenly came alight. 'We can't just stand around. What if one of these opens the door to the outside?'

Tegan looked at the nearest screen. It showed a diagram which she couldn't understand, but which reminded her of the old-time maps which showed the earth at the centre of the universe, long before the spiral-arm backwater that was its true home had ever been imagined. She said, 'Do you think it could?'

'Well, how will we know if we don't try?'

Tegan came around the desk for a closer look.

Kari had been right. Somebody was singing to himself breathlessly, tunelessly, and without much regard for the words. The song was something about being across the purple sea in the cold ground and sleeping peacefully, and the whole endless ramble was basically the same verse over and over with lines skipped, mumbled or hummed. When they came to the end of their tunnel, a cautious peek gave them a view of the singer.

'Who's that?' Kari said.

'He seems happy enough,' the Doctor said. 'Let's find out.'

He was hunched over and limping, obviously very ill. Part of his face, chest and arm had been blackened by an explosion that had ripped open his armourthe same kind of armour worn by their attacker only a short time before. There was a strap around his neck which had been knotted to make a sling for his twisted arm, but despite his injuries there seemed to be an odd cheerfulness about him, self-absorbed and purposeful.

His cloak was spread out on the floor behind him.

There were three or four machine parts heaped on it.

The hood was wrapped around his good hand, and he was dragging the haul onward into the Terminus. It seemed to be a painfully slow business. As they watched, he stumbled and fell to his knees.

The Doctor started to move out of cover, but Kari held him back.

'He's ill,' the Doctor said, and pulled free.

He cautiously approached the man, who was now making a weak effort to get up. Kari emerged from hiding, but she stayed some distance away.

The Doctor said, 'Can I help you?'

The man looked up. He didn't seem surprised.

'Most kind,' he said. 'A burden shared is a burden...

something or other.' And then he handed a part of his cloak to the Doctor, and made it up alone. The Doctor found that he was now expected to join in dragging the machine parts along. The man started singing again.

The Doctor said, 'This isn't really what I had in mind.'

The man broke off his song. 'Oh?'

'I thought you were ill.'

'Ill?' He looked around in case the Doctor might be talking about someone else, but then he shook his head. 'No,' he said, and resumed his dragging.

The Doctor looked back over his shoulder. Kari was, if her expression was anything to go by, getting pretty exasperated. He beckoned for her to follow.

The load was heavy even with two of them pulling, and after a short time the man called a halt. He lowered himself to sit on the floor, exhausted.

'Many thanks,' he said. 'Aid much appreciated. Just a short breather before the, ah, final... whatever...'

'Any time,' the Doctor told him. Now it was time to face Kari. She was looking angry.

'You're breaking every rule in the book,' she said.

'Then we work by different books.'

She held up her useless burner. 'You could have been walking right into danger, and I couldn't have helped you.'

He's harmless. Which is more than I can say for the rest of the wildlife that we've encountered in the Terminus.'

'And what do you think he can do for us?'

'With careful handling, we can get him to explain the set-up here,' the Doctor began, but it was at this point they realised they were again alone. There was only one way that the cabaret could have gone, and the Doctor and Kari moved as one to follow him.

They were expecting to find a further extension of the tunnels, instead they found where the tunnels led: to the engines of the Terminus ship.

They were held in spherical reactor globes, supported in steel cradles with coolant pipes and control cables snaking around, and each had a tiny inspection window. The gla.s.s would be leaded and tinted to near-opacity, but so fierce were the energies inside that each glowed like a tiny sun that is, with the exception of the globe immediately to their left.

This globe was dark and dead-looking.

The man had made it all the way to the far end of the row. This obviously wasn't his first visit, because there was a heap of junk, sc.r.a.p and odd machine parts stacked in front of the globe. Now, ineffectually shielding his face with his arm, he was trying to lift a piece from his latest haul and place it on top.

'There's our radiation source,' the Doctor said.

Kari didn't understand. 'A junkheap?'

'The globe. It's cracked.'

The man managed to add to the pile, but he fell back after the effort. The Doctor and Kari caught him, one on each side. 'Easy now,' the Doctor said, and they guided him to a safe distance and sat him against the support structure of the inactive globe.

'Most kind,' he said. 'I...' he hesitated, and squinted at the Doctor. 'I've seen you before.'

'About a minute ago,' the Doctor agreed.

The man shook his head. 'Short-term memory's the first to go,' he said sorrowfully.

Kari said in a low voice, 'He needs a medic.'

The man heard her, and he looked down at his scorched and damaged arm. 'I tried to pull down the control cables,' he said, 'but I picked the wrong ones.

Power lines. So since I couldn't stop the buildup, I had to wall it in...' he looked towards the heap of sc.r.a.p.

'Only now I'm not sure I'll get it finished.'

'What buildup?' the Doctor said.

'The radiation spill. I used to monitor the levels. My name's Bor. Every time it gets worse, the forbidden zone gets bigger. But this time it's more serious.'

'In what way?'

Bor weakly indicated all around them. 'These are the engines of the old Terminus ship,' he said. 'Know what would happen if one of these exploded?'

'We'd be in big trouble,' Kari said. 'They don't just explode, they chain-react.'

Bor looked at the globe above. 'That's how this one went,' he said.

'I don't think so,' the Doctor said gently. 'The ship wouldn't still be here.'

Kari added, 'None of us would.'

'Oh,' Bor said airily, 'it was a long time ago. And the ship was protected, that's the point.'