Zoe turned back and slumped in the seat, breathing heavily. They were approaching the Dugraqs and the main battle site.

'I didn't disconnect the roof,' she said, as it grated into position around them, 'because I didn't think anyone would be stupid enough to want to use it.'

Jamie grinned.

'Thank you, anyway,' said Zoe.

Jamie began to angle the hover vehicle towards the very recognizable form of the Doctor.

'Oh, and Jamie?'

'Yes?'

'You do know how to stop this thing, don't you?'

Defrabax and the twins walked around the parked vehicle.

'That's quite something, isn't it?' said the mage.

'It would make a fascinating exhibit,' said Raitak.

The Doctor bustled back towards the vehicle, Jamie and Zoe in tow. 'Now, I suggest you all get well away from here. When I activate this gun the Mecrim will think that a huge creature has just hoved into view. They'll stop attacking each other and, with any luck, follow me all the way to the power station.'

'You must let us come with you,' said Jamie.

'No, it's much too dangerous. There have been enough deaths already, and frankly I'm worried enough about Cosmae. You two stay here with the Dugraqs. You've provided me with all that I need.'

'You know how to drive it?' asked Zoe.

'I taught Jamie everything he knows!' said the Doctor proudly. He jumped in behind the steering wheel. 'I've heard the 603 is quite something. Stand back!'

With that he operated the vehicle's hover mechanism, and then pulled the trigger on the gun. A heat-haze immediately surrounded him in the c.o.c.kpit.

The Mecrim turned from their personalized ma.s.sacre and looked up. As one they charged towards the Doctor's flier, tumbling over each other in the excitement. Zoe had never seen them move so fast.

The Doctor rotated the vehicle on the spot, and then sped off into the distance. The Mecrim ran right past the Dugraqs, Taculbain and humans, and were soon lost from sight in the streets of the old colony.

The Doctor glanced between the rear vehicle sensor array, showing multiple blips of pursuing Mecrim, and the computerized bar graph that showed his diminishing speed and power. 'Not far to go,' he said, staring at the approaching power station. 'Just don't let me down now.'

He looked behind just in time to catch a Mecrim making an optimistic leap towards the back of the vehicle. Its claws fell well short, and it collapsed beneath the charging feet of its companions. Moments later it was back in the pack, running at full speed.

A large metal gateway appeared before the Doctor. Had he come this way before? The Doctor never found out if there was a sensor in the gate to facilitate opening as the flier smashed straight into it and careered towards the main reactor building.

Clutching the gun to his chest the Doctor slowed the hover vehicle and then jumped out of the door. He was aware only of the hardness of the ground as he hit it, and the wave of heat that crashed over him as he rolled.

He staggered to his feet, one shoulder feeling very bruised. The Mecrim had come to a halt some yards away from where the hover vehicle had hit a wall. They were confused, but it wouldn't last long. Soon they'd discover that the flames weren't a living creature.

The Doctor ran towards a doorway into the building. It slid open as he approached, the noise making the Mecrim turn. He had to ignore them now, just trust his luck and his judgement.

He ran towards the control room, still holding the gun to his chest. The metal was beginning to blister under the immense heat that was being discharged. The Mecrim were grunting behind him, their feet hammering on the floor - but above even this the ominous groaning of the generators could be heard.

The corridor seemed to stretch for ever, the pursuing Mecrim sounding ever-louder behind him, but the Doctor knew that his emotionally heightened perceptions were not to be trusted. In a rush the control room appeared before him.

The door opened. The Doctor took in the scene in an instant, the android motionless in the corner of the room, Araboam standing behind a shivering Cosmae, glancing nervously towards his lord, and Zaitabor himself sitting at a terminal. His hands were flickering over the keyboard, the screen a ma.s.s of red warning signals. He turned at the expected intrusion. 'Too late, Doctor.'

With no time for words or thought, the Doctor flung the red-hot rifle at Zaitabor and hurled himself to the floor. He felt the rush of the Mecrim as they dived over him and arced through the air, claws and mouths snapping, thrusting their brothers to one side as they fought to attack the huge, mysterious creature first. The silver-grey Mecrim hit Zaitabor just as he stabbed the last b.u.t.ton.

The room exploded in an enveloping, shattering red heat.

Twenty.

Jamie and Zoe were still some distance from the power station when they felt the explosion and saw the flames stab through the windows. Without a word they started running.

Zoe knew that somehow the Doctor had done enough to prevent the explosion of the entire power plant: the fact that they were alive was proof enough. But what had happened?

After what seemed like an age they found themselves running along the corridor towards the control room. Part of the ceiling had collapsed, and Jamie had to help Zoe over the rubble. Beyond that a huge metal beam had fallen against the control room entrance, but Jamie was in no mood to be stopped. He heaved at the post until the door was cleared, and then dropped to his knees to move the debris away from the door. The opening mechanism alternately groaned and sighed, Zoe tugging at the door until it finally started to move.

They darted through the gap and saw two storeys of rubble covering the room, the computers and chairs lost beneath a new landscape of stone and pipework.

In the corner an arm protruded from a pile of small grey bricks. Jamie ran to it and tugged it free from the rubble.

Nothing was attached to it, the stump terminating in wires and hydraulic tubes. Jamie kicked more of the bricks away with his boots until the smashed face of the android was revealed, a mock-human visage visible beneath a feeble mask. A voice crackled from somewhere in the android's throat, but the lips had stopped moving. The eyes were closed, as if in sleep. 'Thank G.o.d for that. I thought that -'

The android didn't speak again.

'Jamie, over here,' called Zoe. She was knee-deep in loose rubble, throwing great chunks into the air with her hands.

Jamie ran to her side, pulling free the half-covered body. It was Cosmae, white with dust, a huge gash across his face.

He looked feverish, his eyes darting from side to side.

'Stay with him,' said Jamie. 'I'll look for the Doctor.' He began picking his way more carefully over the debris.

Someone was coughing to Jamie's right. He ran to the spot, and saw a small figure emerging from a tangled mess of table legs and computer parts.

'Doctor!' exclaimed Jamie. 'You're all right.'

'Yes, thank you, Jamie,' he said, wiping his hands on a large blue handkerchief. 'I think I'll survive.'

'And Zaitabor?'

'He and the Mecrim took the full force of the blast.' The Doctor pointed towards the largest pile of blackened stonework. 'I'll explain later. Are you and Zoe all right?'

'Aye, we're fine. I think Cosmae's been badly injured, though.'

'Let's have a look at him, then,' said the Doctor, nimbly moving over the jagged concrete blocks.

Zoe was sitting at the young man's side, holding his pale hand. Cosmae's eyes were now half-closed. The Doctor put a hand to his forehead, and then felt for a pulse. 'His heartbeat is very weak,' he whispered.

'You're safe now, Cosmae,' said Jamie. 'Just don't give up.'

They watched over the boy for some time. Zoe knew his legs or even his back could be broken, but it was impossible to tell and she had no desire to aggravate his injuries.

Occasionally he cried out, and the Doctor and Jamie held him as firmly as they could to prevent him from hurting himself on the rocks. But it was clear that the light of life was fading from his eyes.

A few minutes later the Doctor stood up and breathed heavily. Zoe sat and stared at the boy's face, her mind numb.

'The Taculbain and Dugraqs will be here soon,' she said quietly. 'The old man will doubtless arrange the funeral.'

Jamie stood up, his teeth clenched.

'I'm . . . sorry.' The voice came from the far side of the room, the speaker stumbling over the inadequacy of the words.

Jamie turned and saw the bruised form of Araboam stumbling towards them over the shifting debris. His armour was dented and scratched, and blood was trickling from a wound in his side.

Jamie ran towards him and grabbed his arms. 'You're what what?' he shouted.

'I must have been mad,' said Araboam. 'I've fallen so far from what once I believed.'

Jamie shook the knight like a rag doll. 'You were involved in all this! So you should have died, not Cosmae!'

Araboam began to say something, but for the second time that day Jamie clubbed him to the ground. He fell on to the unresisting body, still punching feebly at the man's head. 'It should have been you,' he said, as the tears finally came.

'You're the one who should have died.'

The Doctor and Defrabax were talking outside the ruined power station. They were the calm centre in a storm of activity as Dugraqs rushed to and fro, clearing the control room of rubble to ensure that all the Mecrim were dead.

'So what happened?' asked Defrabax.

'When I asked the android to pursue Zaitabor I also wanted to make sure that no one would tamper with the power station. Some explosives were installed that would trip in just before the main generating system went critical.'

The Doctor looked slightly apologetic. 'I meant to warn everyone about their existence, but it seemed to me that only a madman would try to use the power plant again.'

'And that's what happened.'

'Yes. When I realized that Zaitabor was going to use the power station to destroy the entire city I hoped that perhaps the smaller explosives would take care of the remaining Mecrim too. I was very lucky, and it worked.'

'What danger were we in from the Mecrim creatures?'

'It's difficult to say,' said the Doctor. 'If they were to become established in an area and begin to breed then your entire world might have been in serious trouble. In any event a lot would have depended upon the cooperation of the various societies on the surface.'

'Our world is very fractured, very insular,' said Defrabax.

'I hope that one day we shall all mature.'

'The other danger was the plague,' said the Doctor. 'I'll run some tests to make sure that you're not in any danger.

And I'll check up on Jamie and Zoe when we return to the TARDIS.'

'TARDIS?'.

'My vehicle,' said the Doctor.

'Then you'll be leaving us soon?'

'Yes,' said the Doctor. 'There's always work to do somewhere else.'

Defrabax looked around him at the city of miracles again, still scarcely believing his eyes. 'I can guarantee that for weeks to come I will dream of nothing but the other lands and worlds that you have seen.'

The Doctor clapped Defrabax about the shoulders. 'Never lose your dreams,' he said. 'But in future try to dream in patience, there's a good fellow.'

'Wise words. If I had been more patient perhaps Cosmae would still be alive.'

'You don't know that for sure.'

'No. But I feel that I contributed to the lad's death. His mother will sleep less soundly in her grave tonight.'

'I sent Jamie up to explain things to Kaquaan,' said the Doctor. 'Told him that'd be more constructive than beating Araboam to a pulp.'

Defrabax nodded. 'I gave him directions to my house. If she isn't there now, she will be soon. Although she hardly knew him a couple of days ago, terrible events do draw people together. I hope she'll get over the shock and the sadness.'