'Nyssa... that man in the TARDIS...' She paused to get her breath back. 'I don't think he is the Doctor.'

'But he is is! The transmat process induced a regeneration.'

'What!'

'Don't worry, I know all about regeneration.' The Brigadier, striding purposefully up behind Tegan, spoke like a midwife rea.s.suring a nervous father-to-be. 'I've seen it all before.'

'So have we, and the Doctor almost died.'

'Come on,' said the Brigadier, and disappeared into the TARDIS.

'Who is that person?' asked Nyssa, registering Lethbridge-Stewart for the first time.

'Brigadier Lethbridge-Stewart, of course. Come on!'

The Brigadier stood in the doorway of the control room and smiled; it was good to be on board again.

A figure in a familiar red coat stood watching the screen on the far side of the console.

'Doctor!' The Brigadier held out his hand.

The man in the Doctor's red coat turned slowly. Tegan and Nyssa, running in behind the Brigadier, screamed.

The injured creature from the transmat capsule had recuperated amazingly. But he was nothing like the Doctor as any of them had ever known him, with his bulging reptilian eyes, his high domed forehead and slimy flesh that crept and quivered like a stranded fish.

They confronted an alien.

5.

Return to the Ship It was one of the hottest days of 1983 and the Brigadier was sorely in need of a rest. But the Doctor urged him faster and faster up the hill to the obelisk.

'Don't you see, Brigadier? The TARDIS came to Earth in 1977, and so did the transmat capsule, carrying someone - or something - from the ship in s.p.a.ce.'

'And Tegan and the other girl think - or thought - that it was you?'

The Doctor was losing patience. After all, the man had been in contact with Tegan and Nyssa in 1977 when the alien arrived on the first visit to Earth of the transmat capsule. 'You were there, Brigadier!' He spoke as calmly as he could. 'You tell me!'

The Brigadier recoiled, like a child presented with the dentist's drill. 'No, Doctor! Please don't make me remember!'

'You must! I need to know what happened so I can protect Tegan and Nyssa!'

The Brigadier knew he had failed his old colleague.

'Even if I wanted to I couldn't recall any more.' He wished he could explain the inpenetrable barrier that walled off part of his mind.

The Doctor put a friendly arm on his shoulder. 'We could have reached the cause of your nervous breakdown.'

'Good heavens! Do you think so?'

The Doctor was thinking that an experience which had been traumatic enough to give Brigadier Lethbridge-Stewart a nervous breakdown must have been terrible indeed. 'Come on! We've got to get to the capsule before Turlough works out how to operate it. It's the only way I can contact the TARDIS!'

It was beyond the Brigadier's comprehension how a boy from the sixth form could understand the mechanism of a transmat capsule (whatever that might be). But, what was more to the point, neither did he know how he was going to make it to the top of the hill without collapsing in an undignified heap. He struggled to keep up with the Doctor.

The Doctor could already see Turlough kneeling beside the transmitter. They were just in time. He increased the pace, leaving the asthmatic Brigadier behind him.

Turlough had been relieved to discover that the transmitter was not as badly damaged as he had feared. It would be quite possible to cross-patch one or two back-up circuits, subst.i.tute components from the camouflage function for those damaged in the location transmission section and...

'Where did you learn about transmat radiology?'

Turlough had been too engrossed to notice the approach of the Doctor who now stood behind him. He spun guiltily round. But the Doctor was already opening his tool-box from which he selected several pieces of equipment.

The Doctor explained how the police box had materialised in the wrong time-zone as he started work on the broken cylinder. Turlough was amazed that anyone should have such an intuitive understanding of the complex microcircuitry and was fascinated by the Doctor's modifications. Of course, he was trying to contact his TARDIS which was within a few yards of where they were standing, but six years in the past. Surely, contact was impossible? And yet...

Neither Turlough nor the Doctor noticed a panting Brigadier beside them. In normal circ.u.mstances Lethbridge-Stewart would have sent Turlough back to school with a flea in his ear. In fact he said nothing, but stared at the silver sphere between the two trees; it would seem Ibbotson deserved an apology.

Turlough was impressed. The Doctor had arranged for the beam to be reflected off the ship in such a way that, with the warp ellipse absorbing the time differential, it would activate the communications system of the TARDIS in 1977.

'Will it work?' asked the Brigadier bluntly.

'Always the optimist,' sighed the Doctor without looking up.

Turlough grinned. The Doctor went even higher in his estimation.

'By the way, I think this is yours.' The Doctor had been fishing in his pocket for another tool and the crystal cube had fallen to the ground. He picked it up and threw it at Turlough, who caught it as if it were a red-hot coal.

As he stared compulsively into the translucence, he felt a surge of pa.s.sionate hatred for the young man kneeling in front of the transmitter. The Doctor must be destroyed The Doctor must be destroyed!

'You're not the Doctor!' Tegan challenged the alien in the TARDIS control room.

'You travel with a Time Lord and know nothing of metamorphosis?' Mawdryn was playing a deadly game of bluff. At all costs he must convince the tall Earthman and the two girls that he was the Time Lord.

'It wasn't like this before.' Tegan glared disbelievingly across the console. 'When the Doctor changed, he was human!'

'Is a Gallifreyan human?'

'He was... normal!' She looked in disgust at the features of the creature from the capsule.

Mawdryn had nothing but scorn for the purblind Earthwoman. 'What do you know, prattling child, of the endless changing!' he sneered.

'I know that when the Doctor regenerated he didn't turn into an alien.'

'The transmatting induced a mutative catalysis.'

Tegan felt less sure of herself and turned to Nyssa. 'Is that possible?'

'I don't know... it could be.'

Tegan appealed to the Brigadier who was as confused as Nyssa. 'I've seen this happen twice before - different each time.' He shook his head, reluctant to believe that such an unattractive creature was the latest incarnation of his old friend. But he had to agree that, logically, it could be the Doctor.

'The condition will remain unstable,' continued Mawdryn. 'The trans.m.u.tation can be modified, but not in the TARDIS.'

This sounded very plausible to Nyssa who, mistakenly, a.s.sumed he was referring to the zero room, the healing central chamber of the TARDIS, that had had to be jettisoned on the way to Castrovalva.

'We return to the ship,' Mawdryn announced.

'The ship? But we can't leave Turlough,' protested Tegan. 'He doesn't belong in this time-zone.'

'Turlough?'

The boy who came with you in the capsule.'

'There was no boy,' replied Mawdryn, irritated at this sudden irrelevance. He instantly regretted such impatience.

His answer made Tegan suspicious. 'If you're the Doctor you should have transmatted to Earth in 1983. This is 1977!' she challenged.

'Any escape from a warp ellipse can cause temporal anomalies,' countered Mawdryn.

'It's true,' whispered Nyssa to Tegan. 'That's what must have happened to the TARDIS.'

Tegan was not in a position to argue and Mawdryn was grateful the Earthchild was as ignorant as she was aggressive. He tried to smile, though such a contortion of his hideous features produced only a frightening leer. 'I need your a.s.sistance to return the TARDIS to the ship.' He strove to keep the tension from his voice.

But no one moved to prepare the time machine for dematerialisation. Nyssa, Tegan and the Brigadier were stranded in a no-man's-land of uncertainty, half-believing that the mutated being was the Doctor, desperately in need of their help, and half-convinced that he was a dangerous imposter.

Mawdryn trembled; so much was at stake. If only he could get the TARDIS to the ship. If only the genuine Time Lord would follow in pursuit. He struggled hard to remember the names he had heard the man and the two girls use to each other. 'Tegan! Nyssa! Brigadier! My old friends!' he pleaded. 'Please help me!' He leaned, exhausted, against the console. Tears of frustration flooded his eyes.

Tegan and Nyssa looked helplessly towards the Brigadier, who had already made up his mind. If there was the remotest chance that this fellow was the Doctor, he had to be given the benefit of the doubt. Nyssa moved to the control panel.

'Do not enter new co-ordinates. Activate sequential regression,' ordered Mawdryn.

Nyssa obeyed. 'We're ready to leave, Brigadier.' She hesitated to close the doors.

'I'm coming with you.'

'But Brigadier...'

'Don't argue!' He silenced the two civilians, both of whom were only too glad of his company.'

The double doors were shut, the co-ordinate settings reconfirmed, all checks completed and Nyssa's hand poised over the dematerialisation control, when the drone began.

It was a sound they had never heard before.

'Not another alarm?'

'I don't know,' said Nyssa moving round the console. I think it's from the communications system.'

The Doctor stood up, looking rather pleased with himself; the transmitter was working. Already the signal should be reaching the TARDIS. 'Tegan and Nyssa can use the beam as a beacon,' he explained to the Brigadier. 'If all goes well the TARDIS will reappear... Oh no!' He stopped. 'Quickly, Brigadier!' He grasped the old soldier by the shoulders.

'Think! Did you go on board the TARDIS with Tegan and Nyssa?'

'I can't remember. Does it really matter?'

'Of course it matters! Can you imagine what would happen if you walked out of the TARDIS in 1977 and met yourself in 1983?'

'That's ridiculous.'

'Not ridiculous, but almost certainly catastrophic.'

'You mean I could be two people?'

'Certainly.' The Doctor tried to impress upon the bemused Brigadier the seriousness of the Blinovitch Limitation Effect. 'You could exist twice over, but because you're basically the same person any close contact would short-circuit the time differential created by the journey in the TARDIS. The energy discharge would be entirely unpredictable.'

The Brigadier struggled hard to remember what had happened when he and Tegan reached the top of the hill in 1977. From the darkness one faint, misty image emerged; a vanishing TARDIS... he was left beside the obelisk... alone!

He tried to explain the distant, curiously upsetting recollection to the Doctor.

Neither of them saw Turlough dart forward to the buzzing transmitter. There was a noise like a firecracker and the Doctor swung round from his conversation with the Brigadier to see a small whisp of smoke over the apparatus. He rushed forward to inspect the damage.

It did not take him long. 'We won't be going to the ship,' he announced.

'The transmitter is useless. I've lost all contact with the TARDIS.'

The Doctor's dismay was nothing to the relief of Mawdryn when the drone in the TARDIS stopped sounding; any communcation from outside would be disastrous to his plans. 'Dematerialise!' He commanded.

Nyssa prepared to obey.

'Wait!' Tegan held back her fellow companion. 'If that sound came from the communications system, someone might be trying to get in touch with us.'

The girl was not as stupid as her brashness suggested.