K9 followed her.

Spiggot, who had overseen this exchange from the doorway, emerged into the corridor. Although he was now without a weapon, he was determined to see this case, the most baffling of his career, through to the end. He set off after K9.

Stokes hung back. He looked longingly at the TARDIS.

'Why don't I,' he told himself, 'just wait in there?'

He squinted to read the notice on the door of the time-s.p.a.ce craft. 'Pull to open. Right.' He grasped the handle on the right-hand door and pulled. The door refused to budge.

'I knew that was going to happen,' said Stokes. 'Oh well.'

He hurried out of the repair bay.

Gently, the Doctor eased out the last of the thin red rods that formed the core of the bomb. He returned the sonic screwdriver to the pocket of his jacket, and exchanged it for his somewhat battered paper bag of jelly babies. With difficulty, he popped a yellow one into his mouth, and chewed to aid his concentration. The outlook was bleak.

'Well, Doctor,' he told himself. 'You're stranded in a survey base, away from the action. You've lost Romana, K9 and the TARDIS, and your only means of escape is to walk across two hundred miles of sludge in an atmosuit that'll increase your bodyweight threefold. Shouldn't take you a week. Landed, stranded, diddled, dished and done.'

The sugar released by the now chewed jelly baby raced through the Doctor's metabolism to where it was most needed.

Instantly inspiration came. 'Ah!' he cried. 'Now, what about the transmat?'

With renewed enthusiasm, he hopped out of the survey room.

In the gallery above the room where he had imprisoned Xais, Pyerpoint stirred. He was covered in shards of gla.s.s that tinkled off as he righted himself. His left arm flopped, broken and limp, at his side. He fought down the pain and stood up, grunting with exertion.

His head throbbed, and blood smeared the left side of his face where the sharp point of a fragment of gla.s.s had opened his forehead, but these appeared to be his only injuries.

He felt for the laser pistol tucked into his waistband and staggered from the room.

The hum of active machinery led Xais to the mineral stores.

The end of the corridor widened out to form a small, brightly lit chamber. One wall was white and featureless. The other was lined with about thirty small storage hoppers, arranged in three storeys. Each hopper had a clear panel at the front. Each container was filled almost to capacity with silver dust. Raw helicon, sucked from the mountains and the surrounding rocks and pools by robots and bugs, and sifted clear into the hoppers by automated shakers.

Xais let out a moan of ecstasy. She crossed to the nearest hopper and leant her head against it. She could hear the helicon inside calling to her. The itch in her forehead returned and her eyes reddened. The time was approaching. The problem of how to flee this planet afterwards remained, but she knew she would find a way.

And in just a few hours, the activation process would be complete. Every last molecule of the helicon stored here would be infused with her life-force. She could shape it however she chose. Then would begin her revenge on the Normals.

She reached out for the environment control panel next to the storage computer and instructed the hoppers to decrease their internal temperature by hundreds of degrees. The computer reported that the helicon would reach liquid point in six minutes.

'Mistress,' an irritating, tinny voice called from behind her.

She turned from the hoppers to see K9 and the two Normals approaching. She was amused to see that one of them was the cowardly artist from the Rock.

'Stokes. It is fitting that you should be here at this moment in history.'

'No it b.l.o.o.d.y isn't,' Stokes said.

Xais ignored him. 'I may need you to shape the pattern for a new body.' She raised a hand to her mask. It responded to her touch, moulding itself under her fingertips like wet clay.

'My skills with this substance are improving. I am starting to wonder if there is anything I cannot achieve, given time.'

Spiggot put his hands on his hips. 'Come on, Xais. The game's over. You'd best come quietly.'

'Idiot.' Again she tried to send a beam of energy towards them, and again failed. The host was blocking her, conserving its energies for moments of stress in a skilled way that Margo never had.

Frustrated, Xais reached for a control on the wall beside her. With a solid clunk, a ma.s.sive shield slid down across the entrance to the storage chamber. K9 darted forward but was too late.

Xais nodded, relieved, and returned her attentions to the helicon. Bubbles were forming already at the bottoms of some of the containers.

Spiggot slammed the flat of his hand against the shield, howled, and sucked his fingers. 'She's got us licked.'

Stokes asked nervously, 'What exactly is she doing in there?'

K9 answered. 'My sensors indicate that she is lowering the temperature of the inert helicon in order to effect a chemical change in its const.i.tution. This change will render it suitable for activation by the,' he clicked and whirred, searching his vocabulary, 'radiation that she is able to release.'

'So what are we going to do about it, then?' cried Spiggot.

'Stand here talking about it?' He collapsed against the wall.

'There's nothing we can do.'

K9 inspected the shield separating them from Xais.

'Negative. This shield is composed of steel. My laser can penetrate.' He extended his nose laser and started to cut away.

The beam moved with frustrating slowness. To Spiggot it seemed as if the ray was having no effect at all.

Back at the McConnochie Mining base, the Doctor completed his one-handed adjustments to the transmat. He hoped to divert the beam in the direction of Pyerpoint's mine.

'Hmm,' he observed, 'direct non-terminal transmat travel's a good few centuries ahead of this lot. If they only knew it was a simple matter of cross-hatching the pentalion drive with the guidance a.s.semblers, and adding a verification tangle after the seventy-seventh pulse. But people never can see the obvious.'

He flipped up the transmat's timer controls, set the beam to activate in fifteen seconds, and hopped enthusiastically onto the transmission platform.

A dreadful doubt entered the Doctor's mind. 'I hope I remembered to step up the scale on the proton screen. It would be very undignified to be stuck to this chair for the rest of my days. Still, too late to check now.'

He felt the familiar tugging sensation of transmat travel and the warble of the disa.s.semblers. He shrugged his shoulders.

'Oh, that this too too solid flesh would melt...'

And was gone.

Stokes tugged at Spiggot's sleeve. 'Why don't we just go back to that TARDIS?' He gestured to K9. 'He hardly seems to be having much luck on the shield. As you say, we're finished here. There's nothing we can do.'

'You're right.' Spiggot knelt to address K9. 'We've got to evacuate. Let's go back to your box, right?'

'Negative. I must rescue the Mistress.'

Spiggot tapped him on the head. 'You know that's dumb.

But me and Stokes are getting out of here.'

'Impossible,' said K9. 'The door of the TARDIS is locked.

And if I were to open it, you would not be able to operate the systems.'

Spiggot frowned. 'You're coming back with us, K9. That's an order.'

'I am not programmed to accept your orders.'

'The robot revolution has come at last,' said Stokes. 'And, of course, I have to be right in the middle of it.' He crossed to K9 and shouted down, 'I hope you rust.'

'That's no way to address my dog,' said a voice from behind them.

Spiggot and Stokes whirled round. K9 clipped off his beam and swung about joyously. 'Master!'

The Doctor nodded a greeting. 'h.e.l.lo, K9. h.e.l.lo, Mr Stokes.' He turned his most withering look on Spiggot. 'h.e.l.lo, cretin. Ruined any good plans lately?'

'Now, come on, that was hardly my fault,' Spiggot protested.

The Doctor waved him into silence and crossed to the shield. 'The Mistress is behind this barrier, Master,' K9 informed him. 'She is possessed by Xais. I am endeavouring to break open the shield before she can activate the helicon.'

'Good dog. You carry on.' The Doctor looked about.

On the wall to the left of the shield was a small microphone. He reached up with his free hand and unclipped it.

'Here, Doctor,' said Spiggot. 'You're tied to a chair, you know.'

The Doctor ignored him and switched on the microphone.

The helicon was starting to reach activation point. A gentle percussion of freezing bubbles against gla.s.s filled the storage chamber. Xais smiled. Her eyes opened. They were now a vivid blue. Her concentration was absolute. In just a few moments she would begin the process.

An amplified cough disturbed her serenity. 'Er, h.e.l.lo, testing, testing, one two three.'

Her mouth twisted. 'Doctor!'

'h.e.l.lo,' said the friendly voice. 'That sounds like Romana.

How are you, old thing?'

'Your attempt to reach her is futile, Doctor,' said Xais. 'I have total control.'

When the Doctor's voice spoke again it was with considerably more gravity. 'Xais. Listen to me. I know you have endured much. Your entire people were wiped out.'

'I do not want your sympathy,' she called back. 'You are a Normal. Your words mean nothing.'

'Well, at least do this for me, Xais, if you can. Use Romana's skills to work out the likely consequences of your actions. Can you control so much of that stuff? I doubt it. Even if you can, what then? There's no way you can leave this planet, Xais. Your escape route is gone. You'll be trapped here forever.'

At a junction not far away, Pyerpoint stood nursing his broken arm. His blood-soaked face was turned to a screen built into the wall. It displayed the interior of the storage chamber.

Pyerpoint shook with delight, remembering the plans of the mine pa.s.sed to him by its designer, his former accomplice Voltt. Xais was exactly where he wanted her. He could still triumph.

He licked his lips and hurried towards the storage chamber, gun in hand.

The Doctor looked anxiously down to where K9 had almost blasted through the shield. The hastily improvised plan he was about to put into action was gambling all their lives. But he could see no alternative.

'Here's the deal, Xais,' he said. 'You give me Romana, unharmed. I'll give you another host and transportation off this planet in my ship, the TARDIS. I'll take you out of this system. And don't imagine you'll be able to kill us and leave in the TARDIS. You'd never be able to operate it. It contains a field that nullifies all hostile action. Ask Romana to verify that.'

A few seconds pa.s.sed as Xais considered. 'It is so. But these terms are not good enough, Doctor. You must take the helicon also.'

The Doctor licked his lips. He had antic.i.p.ated this request, and deliberately not mentioned the helicon in his offer so that he would now appear to be giving ground. 'Very well,' he said with feigned reluctance. 'We'll load it aboard.'

'And my new host form,' Xais continued. 'I want you, Doctor, to wear my face. That way I will know there will be no tricks on your part. Is that agreed?'

The Doctor, surprised, clicked off the microphone and thought over the stipulation.

'You can't do it, Doctor,' said Spiggot. 'Let me be the host.

I reckon I could show Xais a thing or two. I've been programmed to resist brainwashing.'

'You haven't a brain to wash,' said Stokes.

The Doctor reopened the channel. 'All right, Xais. I'll give myself as host. Until we reach the planet of your choice.' He paused. 'Now, why don't you open the shield and we can begin?'

Before Xais could reply, a high-pitched squawk came from behind the Doctor. He turned to see Stokes, who was held in an arm lock by Pyerpoint. The thin end of a laser pistol had been jammed against the artist's flabby neck.

'Don't move, Doctor!' Pyerpoint warned. 'Or I'll kill him.'

'Oh G.o.d, oh G.o.d, oh no, oh no,' Stokes wailed.

'Shut up,' Pyerpoint ordered him, jabbing him with the pistol to underline his point.

It looked as if Spiggot might be about to jump Pyerpoint, so the Doctor pulled him back hurriedly. 'What do you want exactly?' he asked.

'What I've always wanted,' Pyerpoint replied. 'A return to decency and social order.'

Stokes yelped again.