'Turlough, of course,' said Turlough mischievously.

'Heard about you from Tegan,' said his future maths master.

So this, thought the Brigadier to himself, was the famous Turlough. Just wait till the boy got to Brendon.

He'd have that impudent grin off his face.

'I've come to take you to the Doctor,' continued Turlough insolently.

'The Doctor? You know where he is?'

'Of course. Come on.'

'Not so fast,' growled the Brigadier. 'And keep in the shadows. We've got some disagreeable fellow pa.s.sengers.'

Turlough was far more afraid of the mutants than the Brigadier, but he was keen to score off the military man in the blazer. 'They're harmless,' he jeered. 'You're not afraid, are you?'

The Brigadier could have boxed his future pupil's ears for cheek, but he said nothing and followed the boy in the direction of the Hall of Likenesses. 'What does this Doctor look like?' he asked as they walked past the icons.

'Older than me. Younger than you.'

'I mean, is he... normal?'

'Of course.'

'Then that deformed creature in the TARDIS was an imposter!'

Turlough stopped at the open door of the dormition chamber. 'Doctor? The Brigadier's here.'

The Brigadier peered over Turlough's shoulder. He pushed the boy aside and stepped into the inner room.

'Doctor?' He wrinkled his nose at the faintly rank odour, akin to overipe pheasant, that hung about the chamber.

'Doctor?'

There was a rumble and a click. The Brigadier spun round to see the entrance behind him sealed. The wretched boy had led him into a trap.

'We are scientists,' explained the mutant leader to the Brigadier as he tried to hurry the Doctor to the safety of his TARDIS. 'The Doctor can help us only of his own free will.'

'You cannot ask me to change my whole nature,' the Doctor repeated stonily as Mawdryn pleaded with him to end their infinite journey.

'Come on, Doctor, we're getting out of here,' whispered Tegan.

But still the Doctor lingered by the regenerator. He could not believe he was destined to escape so easily. 'You have the regenerator and the facilities of the laboratory.

Continue with your experiments. Find how to reverse the process.'

'We have known for many years that the process is irreversible.'

Nyssa moved to the Doctor's side. 'There must be something you can do to help them.'

'Don't interfere!' The Doctor silenced her angrily. 'I cannot will my own destruction.'

'So be it,' said Mawdryn wearily. 'Leave now with the rest of your companions. But accept the consequences of your own actions.'

The other mutants began to murmur in protest. 'Go quickly,' urged Mawdryn.

'That sounds like good advice.' The Brigadier grabbed the Doctor by the arm and propelled him towards the door.

'We have experimented for centuries,' clamoured the mutant lying next to Mawdryn.

'We have tried to discover a remedy,' cried his companion.

'There is no remission,' moaned another in despair.

'Only the power in you, Time Lord!'

'Only you can help us, Doctor. Share the life-force with us, that we may grow old and die!'

The Doctor stood watching them like a sailor who has seen his shipmate fall overboard, and knows that, while the boat sails on, the castaway must surely die.

'Come on, Doctor,' urged Tegan. 'There's nothing that any of us can do.'

The Doctor turned reluctantly to go. Filled with dismay, the mutants struggled to free themselves from the regenerator.

'To the TARDIS, the lot of you!' roared the Brigadier and shepherded the Doctor, Tegan and Nyssa out into the corridor.

The mutants howled like abandoned children and would have rushed into the pa.s.sageway to drag the Doctor back into the laboratory had they been strong enough.

'My friends, do not despair,' Mawdryn comforted his fellow exiles. 'The Doctor will return, and of his own free will.' He detached himself from the machine and stood, tall and strong, as any normal creature. Only the ulcerous sarcoma on the right of his face branded him as unnatural.

'There is work to be done,' he announced gravely. His seven comrades looked at him, hardly daring to hope.

Then he spoke the words they had waited over two thousand years to hear. 'Prepare our ship for the ending!'

As they rushed along the sombre corridors towards the TARDIS, Tegan noticed how out of breath the Brigadier was getting. The poor man had certainly gone to pieces in those six years since she was at Brendon School put on weight too, she observed, as he paused to get his breath back. 'I'm Tegan by the way,' she said, introducing herself with a friendly smile. 'We have met, but it was rather a long time ago.'

'Miss Jovanka, could I ever forget,' puffed the breathless Sir Galahad of Jubilee Day.

'Doctor, what are we going to do about Turlough?'

asked Nyssa.

'Turlough will have found the TARDIS by now.'

'And the other Brigadier?'

'I can only deal with one Brigadier at a time!' snapped the Doctor, desperate to reach the police box and get clear of the alien ship.

'What's that?' Lethbridge-Stewart p.r.i.c.ked up his ears.

The Doctor explained to the horrified old soldier the presence of his six years' junior on board Mawdryn's ship.

The senior Brigadier was none too happy about the way the Doctor proposed to leave part of him adrift in s.p.a.ce.

'You were perfectly all right in 1983,' the Doctor explained impatiently. 'Obviously your 1977 persona came to no harm.'

The Brigadier, who by now didn't know whether he was coming or going, entered the TARDIS with the two girls, still grumbling about spending six years in limbo.

'No sign of Turlough,' said Tegan, looking round the control room.

'Never trusted that boy,' muttered the Brigadier testily.

'Maybe he's exploring the TARDIS?'

'I hope so,' said the Doctor, already setting a course out of the warp ellipse, 'because we've got to get the TARDIS away from here.'

'Look!' Nyssa pointed to the scanner.

Running down the corridor, terrified that the TARDIS was leaving without him, was Turlough.

Turlough had felt rather pleased with himself at trapping the younger Brigadier so neatly inside the dormition chamber. That would settle a few scores with the cantankerous old pedagogue - albeit prospectively. He grinned at the paradox: the prisoner from 1977 was, as yet, a stranger.

There were no congratulations, however, from the Black Guardian; no voice; no glowing presence. He took out the cube a mere piece of gla.s.s.

Turlough strolled along the marble ambulatories, exploring libraries and galleries, luxurious salons and halls of recreation.

He began to feel lonely. Perhaps the Doctor was already dead; and the girls; and the older Brigadier. He had been abandoned!

He was on the point of returning to open up the dormition chamber - if only for the doubtful company of the junior Brigadier - when he heard the voices.

From behind a gilded b.u.t.tress, he could see the Doctor and his companions, alive and well and on their way back to the TARDIS. Could the Doctor be escaping? Had the Black Guardian failed? Turlough followed at a distance, and saw the Doctor, the girls and the senior Brigadier all disappear into the police box.

It suddenly occurred to the boy that, with the TARDIS gone and the Black Guardian, maybe, defeated, he would be marooned on the ship. He rushed panic-stricken towards the time-machine.

To Turlough's surprise, the Doctor met him in the doorway.

'Turlough, listen very carefully.' An unusually agitated Doctor explained the problem of the two Brigadiers.

As if it were one of Canon Whitstable's anecdotes, Turlough pretended he was hearing it all for the first time.

'Find the Brigadier and take him to the transmat capsule,' ordered the Doctor.

'But the transmat beam doesn't work.'

'The capsule is locked in to the TARDIS homing device. When you operate the capsule it will transmat to the centre of the TARDIS.

Turlough nodded.

'When you arrive in the TARDIS, stay in the capsule.

Don't let the Brigadier out until I tell you it's safe.' The Doctor slammed the door. The light on the police box flashed, there was a grinding sound - and a rather bemused Turlough was alone in the corridor.

The Doctor was delighted to have escaped from the red ship so easily. 'It takes a very cunning setting of the co-ordinates to clear a warp ellipse,' he boasted from beside the console.

The two girls were more subdued. 'Will the mutants really travel for the rest of time?' asked Nyssa.

For some reason the Doctor would not look either of them in the face. 'Sometimes you have to live with the consequences of your actions,' he replied coldly.

'That's terrible.' Nyssa was close to tears; but the Doctor pretended not to notice.

'Doctor!' shouted Tegan suddenly.

'Something's happening,' Nyssa gasped.

'Not at all,' replied the Doctor, still concentrating on his navigation. 'We're on course for Brendon School in 1983.'

'Doctor!' The Brigadier, who had been watching the two girls for several moments, cried out in horror. The Doctor spun round. Nothing could have prepared him for the appalling sight of his two companions.

Tegan's auburn hair had turned white. Wrinkles raced across her face like cracks in thin ice, and her teeth were beginning to leer from shrunken gums; she was suddenly as old as the hills.

Nyssa's skin, too, was a network of puckering pleats and lines, her mouth gaunt and twisted as a crone's.

'What's happening!' shouted the Brigadier.

The Doctor just stared, amazed beyond belief, at the time-worn faces of the girls.

'Doctor, do something!' cackled the senile Nyssa.

'Please... Doctor!' Hardly more than a death rattle came from Tegan's throat.

'Tegan... Nyssa...' stammered the Doctor helplessly.