But before the Doctor could step forward, Rogers was in the doorway. Holding a shotgun. It was levelled at the Doctor's chest.

'The only bit of checking up you'll be doing, Doctor, is in the cellarage.'

Peri watched horrified as Packwood turned to stare at each of them in turn. His eyes lingered on her, his eyes wide and pale with barely a hint of a pupil in the dead iris. She screamed.

Then she turned to run.

And saw the figure behind them, approaching, lurching towards them over the damp gra.s.s of the front lawn. It was Bill Neville, his arms out, dead fingers twitching and clenching as he shuffled towards them. Behind her, Peri could hear Packwood's booming laugh as it echoed off the mist and the face of the building.

The only way out was along the front of the house. If she was quick, while the shotgun was pointed at the Doctor, while the Doctor was between her and Packwood. 'Come on!' she shouted to Sir Anthony and Janet.

But even as she made to run, a hand gripped her arm and jerked her back. 'I don't think so, Peri,' a voice said close in her ear.

Janet's eyes were wide and pale. She blinked rapidly several times as she pulled Peri back into the group. 'I really don't think so.'

Chapter Eleven.

Sheldon's Folly It took a while for Peri's eyes to adjust to the near darkness.

There was some light, filtering dustily through a grating high in the wall. The Doctor strode across the room, apparently oblivious to the darkness. At once he was swallowed up by the darkness as Peri and Sir Anthony stood nervous and tentative by the door.

'Well, if this is the best cellar you've got, I'm not terribly impressed,' the Doctor proclaimed loudly. The only reply was the sound of the bolt shooting home on the other side of the door, followed by retreating footsteps.

As Peri's eyes gradually managed to cope with the gloom she looked round. The corners and edges of the cellar room were still shadowed and lost, but she could just about make out the stone slabs of the floor and the complete lack of furnishing. Apart from what looked like a low bed against one wall, a slab of dark silhouette against the deeper shadows.

'Is Janet...all right?' Sir Anthony asked quietly.

'Of course not,' the Doctor told him shortly. 'But I don't think she's yet as far under the influence as she would have Packwood and his cronies believe.'

'She'll help us then?' Peri asked.

'I don't think it's up to her,' the Doctor said. He sat down cross-legged on the floor and started to empty the detritus from his pockets. 'It depends how much control what's left of her free will has over her body. And that will be less and less as time goes on.'

'Great,' Peri said. She kicked at the floor. Then she froze as, out of the corner of her eye, she saw the shape that was the low bed begin to stir.

The Doctor was refilling his pockets. 'Nothing much here of use,' he admitted glumly. 'I think we're in for a long stay.'

'Doctor,' Peri whispered. The shape on the bed was rising, staggering to its feet now 'Doctor!'

'Quiet, Peri, I'm thinking.'

'Doctor, I think you should come over here.' Sir Anthony had seen it too. And now there was the sound of the blankets and sheets tumbling to the floor as whoever or whatever was in the bed emerged and staggered towards them.

The Doctor turned, and visibly jumped with surprise.

'h.e.l.lo,' he said, no trace of anxiety in his voice. 'Who are you?'

As the figure staggered forwards, Peri could see it more clearly. It was a man, dishevelled and unshaven. He was dressed in tattered and torn clothes, holding his left arm close to his chest, covering it, hugging it with his right arm as he approached. It was the man she and the Doctor had met near the TARDIS, the man who had scared Mike Neville away when he accosted her on the moorland.

'My G.o.d,' Sir Anthony breathed, close beside Peri.

'What's happened to you?'

The figure stopped, as if it recognised the voice. Then slowly the man sank to his knees, rocking back and forth, moaning quietly and clutching his arm.

'You know him?' the Doctor asked as he slowly approached the man and knelt down beside him.

'Of course I do,' Sir Anthony said. 'Doctor, this is Christopher Sheldon.'

As the Doctor knelt beside him, leaned forward, Sheldon twisted away so his back was to the Doctor.

'What's...what's happened to him?' Peri asked.

'I have no idea. Seems traumatised.' The Doctor leaned in, speaking quietly, gently. 'I'm not going to hurt you. We're here to help. Are you hurt? Let me see.' The Doctor and Sheldon seemed to merge into a single dark area of shadow as the Doctor leaned closer.

'Maybe it's his fingers,' Peri suggested. 'He was missing some fingers on his hand. An accident perhaps,' she told Sir Anthony.

The Doctor straightened up, separated from Sheldon. 'It's not his fingers,' he said gravely. 'His arm's been severed.

Amputated. Gone.'

'Good grief,' Sir Anthony said. 'Doctor, what is going on here?' He glanced at Peri, and the two of them joined the Doctor beside Sheldon's huddled form.

Sheldon looked up at them, his eyes were wide and pale in the dim light. He blinked. 'Know you,' he murmured, pointing at Sir Anthony with a clawed hand. As he moved his arm, Peri could see the remains of his other arm hanging loose from his shirt. The sleeve had been cut away, and a rounded stump of upper arm emerged pale and clean from the ragged material.

'Need a chair,' he gasped out suddenly. 'Wheelchair.'

'No, it's all right,' Sir Anthony said. 'It's your arm, not your leg.'

'Arm?' He looked down at the stump. 'Arm. Needed arm.

Took it. Again.'

'Again?' the Doctor asked. 'What do you mean, again again?'

'Keep taking it. Again and again and again and again and - '

'Yes, yes. All right,' the Doctor interrupted. 'I think I get the idea.'

'Better this arm.' Sheldon nodded. 'This is the arm. The arm that opened the sample casket. Did the gathering.'

'Gathering?' Peri asked. 'Does he mean...?'

The Doctor was nodding. 'Gatherer Three, yes I think so.'

He turned back to Sheldon. 'What do you remember? It's very important that you tell us about the casket. That you remember, Mr Sheldon.'

But Sheldon seemed to have collapsed in on himself, huddling closer into the floor, curled up with his remaining arm tight round himself. 'Three-zero-seven,' he muttered.

'Mustn't open three-zero-seven. Mustn't open it. Three-zero-seven.' His voice trailed off into incoherent murmurs and mutterings.

'That was the sample from Gatherer Three,' Sir Anthony said. 'You recall, Janet Spillsbury said -'

'Yes, yes, yes,' the Doctor said, waving him into silence.

'We know that.'

'What did he mean, they took his arm again?' Peri asked slowly.

The Doctor nodded. 'I was wondering that.'

'And?'

'And I don't like what I'm thinking.'

'Care to share it with us anyway?' Sir Anthony asked.

The Doctor stood up and turned towards them. The light catching his eyes and making them gleam as he did so. 'I asked Janet about generation one,' he said.

Peri remembered. 'She said something about an incubator, didn't she?'

'That's right. They would need to cultivate genetic material. Grow it, in effect. In a suitable environment.

Somewhere that the Denarian material would thrive.'

'Like an incubator?'

'Ye-es.' The Doctor was pacing slowly backwards and forwards. 'You know how vaccines and viruses are cultivated in eggs, organic material like that. A nice warm, inviting place for them to grow and mature and thrive?'

'Yes,' Peri said. 'But what's that got to do with -' She broke off as she began to see. 'But that's...'

'Horrible,' Sir Anthony finished for her.

'But it's what I think is happening. It explains why this poor fellow is out of his mind. And there's a certain logic to it.'

'Logic be d.a.m.ned!' Sir Anthony said.

'If Sheldon was the first person to become infected, the Denarian would use him as its initial breeding ground. Like a farm for genetic material. And the others, those with a secondary infection, would know to harvest material from him to form the genetic basis of the infection they pa.s.s on.'

'He was missing fingers when we saw him before,' Peri said quietly. She hardly dared look at the huddled figure on the floor. She was feeling sick.

'Either they just took fingers before, or the arm had already grown back. The Denarian infection would keep repairing the body as they took the material...A self-sustaining source.'

'But...how could they?' Peri's words sounded lame, pathetic under the circ.u.mstances. But she didn't care.

'Oh, I imagine they started with skin samples. Small pieces of material, like an amount of blood for example.

Sheldon would have been a willing contributor in the early stages. It was his project, this dream of a universal cure, remember. But then their needs grew. And the infection within them, within all of them, started to take over. So they started taking more and more. They knew the damage wouldn't be permanent.' The Doctor knelt down beside Sheldon again, patted him gently on the shoulder. 'Except to his mind,' he added.

'And Janet?' Peri asked. 'Did she know?'

'I couldn't say. I doubt she knows it all. Perhaps she thinks Packwood and Madsen are still taking blood samples and skin tissue.'

'Madsen?' Sir Anthony asked.

'He must have been involved,' the Doctor said. 'To perform the operations on Sheldon here. And to pa.s.s on the material. Infect the villagers. Run the experiment.'

'And the longer we're stuck in here, the worse it gets,' Sir Anthony said.

'And the less likely that anyone will come to help us,' the Doctor added. 'Frustrating, isn't it?'

It was as if the mist had somehow got inside her head. Her vision was blurry, unreal. Her thoughts were sluggish and forced. Packwood was talking to her through a fog. Telling her his plans, how well it was going. How they were entering the third generation.

'When did you do it?' she asked. Her voice came to her through water.

'Bring you into the fold?' he asked. 'Ensure that you were protected, like me, from the ravages of the flesh?'

She nodded. Her brain felt loose inside her head.

'Weeks ago. When we first came to the island.'

Janet's head was spinning. A succession of images played out: Dr Madsen telling her she needed a shot of antibiotics as protection. The needle pressing into her arm, puncturing the skin, drawing out a tiny bead of blood. Packwood's rea.s.suring smile - the mirror of his expression now as he stood in front of her.

'You are entering the third generation,' he said. 'I - we - can tell.' He leaned forward, his face distorting in her blurred sight, his grin fish-eye wide. 'Welcome,' he breathed at her.

'Welcome to the fold.'

'You b.a.s.t.a.r.d! How dare you? What gives you the right to treat us - to treat me - like this!' she screamed at him. But the words were trapped inside her mind, unable to find escape or expression.

'Thank you,' she heard herself say. And she felt the darkness beginning to push her thoughts aside as it a.s.sumed control within her mind.

'Do you think they're just going to leave us here?' Peri asked.

It was dark and damp. The light outside had faded and with it what little light spilled into the cellar room had also gone.

'Quite probably,' the Doctor said cheerfully. 'They don't need us, after all.'

Peri did her best to keep her voice level. 'So we're here for...for a while then.'