'What?' the Doctor demanded, leaping to his feet. 'But you...that is...What do you mean?'

Packwood sounded tired. But there was a gentleness, a humanity in him that had been lacking. Only now that he showed those qualities did it become obvious what had been missing. He rubbed at his eyes as he spoke. 'I mean, Doctor, that you haven't killed it. I can still feel it within me, regathering its strength. In a few minutes it will be in control again.'

'A longer dose?' Peri suggested. 'Would that do it?'

'Probably.' Packwood conceded. 'It is weak, frightened, hurt. But there's no point really, is there?' He swung his legs up and lay back on the bed, hands resting across his chest.

'Why not?' Sir Anthony asked.

'I imagine an exposure long enough to kill the Denarian would also kill Mr Packwood here,' the Doctor said quietly.

'Kill and cure. Not really an option, I think.'

'So, what do we do?' Janet asked. Her voice was strained, her face betraying the disappointment that there was no easy cure.

'Make the most of me while you can,' Packwood suggested weakly. 'Before it rea.s.serts itself, I will tell you what I know.' He turned slightly on his side. His face was drawn and gaunt. 'You were right, Doctor, for what it's worth.

This thing - it saps the will, the power to make decisions. I didn't even realise. I thought...I thought it was me, that what it wanted me to think was what I wanted to think. That its thoughts and decisions were my own.' He slumped back again. 'But really, deep down, somewhere, somehow, I knew.'

His body shook suddenly, a sob of anger and misery. 'I can't go through that again.'

The Doctor took his hand. 'Then help us to stop it,' he said. 'There must be a way. Tell us whatever you can.'

'I think you know most of it, Doctor.' His voice was weak, a contrast to the size of his body. 'We started with the chickens. There was no thought at first of a human test, though we brought in Madsen. So even then it knew, was planning, was arranging our thoughts. Otherwise, why would we have brought in Madsen?' He coughed, his body shaking, making the bed vibrate beneath him. 'The island environment was ideal, both for chickens and then sheep. I don't know when it took over, when its thoughts became mine. I see Janet losing her mind, slowly from within. But at least she knows what is happening. That's why it can't let her speak.'

Janet nodded, her brow furrowed with effort and exertion.

'Difficult,' she said indistinctly. 'Want me to say things. Not my words.'

'The process will speed up. Others will succ.u.mb quicker as it learns how the human body and mind work,' Packwood said. 'Learns from within. Communicates with itself across the ether. Don't know how. Not thoughts as such, it just...knows.'

'I think,' the Doctor said slowly, 'that there must be a central source. Someone is host to the main intelligence, a co-ordinating colony of this material that organises the rest of it somehow.'

'Me?' Packwood gasped.

The Doctor raised his eyebrows. 'You do seem the most likely candidate,' he admitted. 'That could be why Janet's infection seems to be marking time, as it were. For the moment.' He cleared his throat. 'So how did you start on the humans?' he asked quietly. 'Tell us what happened.'

'There were problems.' Packwood was struggling now, forcing the words out through clenched teeth. 'Vet died. But that helped as Madsen took over his work. Other adverse - fatal - reactions too as we refined the material. Then the fishermen. One broke his arm, an excuse for Madsen to treat him, and then them all. But their boat was lost in a storm. Bad luck, that.' He coughed again. 'But we still had the children.'

He sobbed again, a racking, shaking cry from deep within. 'Oh G.o.d, the children.'

'The flu jab?' the Doctor asked.

Packwood nodded, a slight movement hampered by his position on the bed. 'Miss Devlin too. After that, it was one by one.'

'As Madsen treated people, so he infected them?

Injections?'

'Yes. In the neck, into the artery. Bloodstream. Usually gave them two, to be certain. Then he tracked how the material coped with whatever illness or complaint they had.'

He was forcing the words out now. 'Good...data...'

'So how come they're all infected?' Peri asked. 'It seems like the whole village was out there.'

The Doctor nodded. 'A good question. Madsen can't have treated them all.'

'No,' Packwood agreed. 'Can be pa.s.sed on by digestion of infected material. Like chicken. Also, developed an oral version. Dispersed it in liquid. Spreads easily. Quickly. Infects everything in the food chain. Not just chickens and sheep.'

'Oh my G.o.d,' Sir Anthony breathed. 'We're lucky we escaped it then. I'm glad I haven't eaten chicken recently.'

'Oral version, only recent,' Packwood gasped. 'Cows.'

'Cows?' Peri said. Her head was swimming again, vision blurring.

'Infected their drinking water,' Packwood said. 'Meant the milk was tainted. Then pa.s.sed on to other animals. Into river water from urine. And on and on.'

Peri swayed, reaching out for the lead screen to steady herself. She was suddenly aware that her cold had not developed, had gone after her visit to Hilly Painswick for tea.

'Milk?' she said weakly. But n.o.body heard her.

Packwood had levered himself into a sitting position. 'You think I am the source of the problem, Doctor?' He was gripping the Doctor's wrist as he asked.

'Well,' the Doctor said slowly. 'It's only a theory. But it fits the facts so far as we know them. I wasn't meaning to apportion blame.'

'Time to move on,' Packwood said quietly, his voice barely audible. 'Before...before it comes back.' He tapped the side of his head. 'While I am still in control in here.' He managed to stand up, shaky but determined.

'The main laboratory,' the Doctor agreed. 'Let's see what we can sort out. There must be a way. Has to be.' He supported Packwood and together they struggled to the door.

The others followed, Peri last, stumbling after them, trying to focus.

Packwood was leaning forwards on the door frame, his head against it, hands either side. The others pushed past into the pa.s.sageway outside. The Doctor reached out to help Packwood.

Packwood stepped back from the door frame, swaying slightly as the Doctor made to help him. But then he pushed the Doctor suddenly away and stepped back into the X-ray room, slamming the door behind him.

The Doctor was at the door immediately, tugging at the handle. But they had all heard the bolts shoot home and the door refused to move.

Packwood's face appeared at the small window. His voice was cracked and faint through the heavy door. 'Only way, Doctor,' he shouted. 'If it is controlled through me, then there is only one way.'

'No,' the Doctor shouted back. 'No, Packwood, listen to me. We can fmd a cure. There must be one. Help us!'

Packwood was shaking his head. 'Too late,' his m.u.f.fled reply came through the door. 'Already losing control again.

Now or never. Last chance. Of freedom. For us all.' Then his face was gone. The Doctor jammed his own face to the thick gla.s.s, watching horrified through the window.

Logan Packwood could barely stand. His body fought against the alien material as he staggered across to the control panel behind the lead screen. He could see that the Doctor had set the intensity level to maximum and overridden the timer cut-out. He twisted the dial, listening with satisfaction to the hum of power through the X-ray machine. Then he staggered out from behind the screen, collapsing in the middle of the floor, letting the cleansing invisible rays wash over him, wiping his body and his mind clear.

He was too weak to move now. He could feel his skin beginning to blister. He felt sick. But also, elated. He had done it. If the Doctor was right, the controlling consciousness of the Denarian was dead now. The material within the other infected people would revert to first generation, mindless, healing. It would evolve, slowly, again. But now the Doctor had the time and the knowledge to deal with it.

He tried to crawl back to the screen, to shelter. Maybe this was enough, maybe he could switch off the apparatus and live out what was left of his irradiated life free of the contagion.

He collapsed back to the floor before he even got close.

The Doctor sighed. For a moment he rested his forehead against the cold gla.s.s of the window. Then he took a deep breath and turned away.

'How do you feel, Janet?' he asked. 'We should know immediately if the Denarian has lost control.'

'Fine, Doctor,' she said at once. Then her forehead creased, her mouth opened, working silently for a while before she was able to gasp out: 'No, not gone. Still... here...inside.'

Outside the house, the villagers surged forward suddenly, as if on an unspoken order. They started on the door, hammering with their fists at the heavy woodwork. Rogers and what was left of Madsen were at the front. Children pushed through and started on the lower part of the door.

Others moved to the windows of the drawing room, oblivious to the smoke from the dying fire within. Hilly Painswick stood beside Old Jim as they battered their fists against the toughened gla.s.s.

The Doctor threw open the door and strode in purposefully. 'I was not wrong,' he exclaimed as he looked round. There was a main table down the middle of the room. There were other work surfaces against the walls. Above one of these was a metal plate set into the wall.

On the far side of the room was a heavy metal door with a keypad next to it. The door had rivets and was braced with more metal.

'Well it hasn't worked,' Peri told him. 'Has it?'

'And now we've lost access to the X-ray machine,' Sir Anthony pointed out.

'There must be another main host. Someone else with the controlling consciousness within them,' the Doctor said.

'Or...'

'Or? Or what?' Peri wanted to know.

'Or I was wrong,' the Doctor admitted sharply and quickly. 'This is not the main lab,' he said thoughtfully as he looked round. 'Or if it is, then I'm more than a little disappointed in the facilities available, though impressed with what's been achieved.'

Behind him, Janet raised her hand. It was a hesitant gesture as if her hand were too heavy for her arm. She pointed a shaking finger at the metal door on the other side of the room.

'Through there?' the Doctor said. 'I see.' He started across the room towards the door, but before he was half way, he suddenly dropped to his knees and looked under the main table. 'h.e.l.lo there,' he said cheerily.

Christopher Sheldon slowly uncurled, his stained face emerging from the ragged folds of his clothes. 'Oh,' he said.

'It's you again, is it?' Carefully, tentatively, he crawled out from under the table and looked at them all. Then, just as carefully and tentatively, he dropped to his knees and crawled back again. As he went, Peri could see that his arm was completely healed, up to the hand, and she shuddered.

The Doctor walked all round the room. As he got back to the door, he pushed it shut and shot the bolts. 'This is it,' he said grimly. 'This is the end of the road. Here we stand, we can do no other.'

Sir Anthony nodded. 'I agree, Doctor. They'll be through into the house before too long. Maybe they won't find us down here.'

'Oh they'll know we're here,' the Doctor said. 'Won't they, Janet?'

Her eyes were wide, the irises already faded almost to white. 'Everything's fine, Doctor,' she said easily. 'There's no problem. You can open the door.'

'She's gone,' Peri said.

'You don't need to lock me outside, Doctor,' Janet said suddenly. There was an urgency in her voice, an edge.

'I have no intention of locking you -' The Doctor stopped suddenly, and peered closely at her. 'Oh,' he said slowly. 'I see what you mean.'

'What are you talking about, Doctor?' Peri asked.

'I think that's Janet's telling us something, am I right?' the Doctor asked.

'Absolutely not, Doctor,' she replied.

'You see,' he said triumphantly.

'No,' Sir Anthony told him.

With a sigh and exaggerated patience, the Doctor explained. 'The Denarian is controlling Janet's body and her speech centres, much of her brain too I suspect.' He looked to Janet.

She shook her head.

He smiled. 'You see, I'm right. She's communicating with us, despite the Denarian, by saying the opposite of what she means. It will let her say things it wants us to hear, but not what will help. But I think it has no sense of sarcasm or irony.'

'What?' Peri asked.

'Like Americans,' the Doctor said tersely. 'She's lying to us, Peri. And because we know that, she can communicate.

Now then,' he went on before Peri could comment, 'tell us, Janet, does that door lead into the main laboratory area?

Where we might be able to get at some useful equipment? It's a bit Spartan in here after all.'

Janet shook her head. 'I'm afraid not, Doctor. You won't find anything useful through there at all.'

'Excellent.' The Doctor beamed, rubbing his hands together triumphantly. 'And I would guess that you know the code to open the door, right?'

Janet's expression was frozen on her face. 'Absolutely, Doctor,' she said. 'Of course I do. Logan Packwood would never have been so arrogant as to keep that entirely to himself.'

The door was withstanding the hammering without apparent damage. It was pitted and battered, but showed no signs of giving way.