They swept up to the junction, the Doctor's foot pressed steadily on the brake, and Bessie stopped instantly.

Jo gulped. 'Why didn't I go through the windscreen?'

'Because Bessie's brakes work by the absorption of inertia - including yours.'

Suddenly Jo's attention was caught by the whirring of the time sensor. 'It's starting again!'

'Come on, Bessie, old girl,' said the Doctor. 'It's up to you!'

Checking that the junction was clear, the Doctor started Bessie up again and shot off even faster than before.

Unfortunately it was a case of more haste, les speed. Just beyond the junction was the notice board signalling the way to the Newton Inst.i.tute. The Doctor and Jo shot straight past without even seeing it. . .

In the TOMt.i.t laboratory, the Master switched on the power. The experiment was about to begin.

'Surely you don't need to wear radiation gear out here, Professor?' asked Ruth.

'A precaution in case of emergency, my dear. I may have to join Mr Hyde in the inner laboratory in a hurry.' He leaned over the intercom. 'Report!'

Stuart's voice came from the speaker. 'Interst.i.tial activity, nil.'

Ruth was placing a rather handsome cup and saucer on the metal transmitting platform. She checked a dial. 'Molecular structure stable.'

'Increasing power,' snapped the Master.

The oscillating whine of TOMt.i.t rose higher. Ruth's voice was tense. 'Isolate matrix scanner.'

'Check'

'Increasing power,' said the Master again.

Ruth gave him a worried look. 'But you're into the second quadrant already, Professor.'

'I know what I'm doing.' The Master spoke more calmly. 'Initiating transfer!' The Master spoke more calmly. 'Initiating transfer!'

He threw a switch and to the astonishment of the Brigadier and the other onlookers, the cup and saucer faded slowly away.

'Good heavens,' said the Brigadier. He looked through the part.i.tion and saw the cup and saucer standing on the receiving platform in the inner laboratory, the radiation-suited figure of Stuart Hyde hovering over it.

Suddenly Stuart's voice crackled frantically from the intercom. 'I'm getting too much power again. I can't hold it. Switch off. Switch off!'

Ruth turned to the Professor, and was horrified to see that he was actually increasing the power. 'Turn it off!' she shouted.

But the figure at the controls seemed rapt, enchanted.

Throwing back his head the Master roared, 'Come, Kronos come! come! I summon you!' I summon you!'

4.

The Ageing

In the inner laboratory the crystal glowed with a fierce, almost unbearable brightness.

Even through the darkened vision-plate of Stuart's helmet it's intensity was dazzling.

He staggered back. . .

Suddenly the transferred cup and saucer glowed brightly, then shattered.

In their place Stuart sensed rather than saw something else beginning to form.

A winged shape . . .

A tendril of fire snaked out, groping aimlessly. It touched Stuart, and his whole body glowed brightly for a second.

He staggered back, clawed at his helmet and collapsed. Beneath the helmet, his face began to change . . .

Ruth saw him fall, and ran to the part.i.tion door. She was about to go to his a.s.sistance then stopped herself. The radiation level in the inner lab was still dangerously high. But Professor Thascalos was already suited up.

She swung round and called 'Professor!' To her horror, she saw that the Professor had disappeared.

Ruth ran back to the main control console. Stuart would have to wait. The essential thing now was to turn off the power - if she could . . .

It didn't take the Doctor long to realise that he overshot his destination. He stopped the car, studied the map and swung the car in a U-turn. Minutes later he was streaking up the drive of the Inst.i.tute and making one of his amazing stops before the main door.

The Doctor jumped out of the car. 'Right, Jo . . . Oh, good grief!'

Jo Grant didn't move or speak. She was sitting quite still, staring straight ahead of her.

For a moment the Doctor thought she must stunned by the speed of the journey.

Then he realised that it was something else entirely that happening - something that confirmed his worst fears. Someone was interfering with time.

As he turned away from the car, he felt the resistance of the temporal disturbance.

Forcing his way through it, the Doctor used the resistance as a guide, letting it lead him to its source. He ran through the archway at the side of the main building, across the courtyard beyond, through the white-painted door on the other side.

In his haste, the Doctor failed to notice a radiation-suited figure, flattened against the wall on the other side of the arch.

As the Doctor vanished through the door the figure s.n.a.t.c.hed off its helmet. His face a picture of frustrated evil, the Master turned and hurried away.

After climbing endless flights of stairs the Doctor dashed into the attic laboratory.

He summed up the situation at a glance. 'Cut the power!'

'I can't,' shouted Ruth frantically. 'The controls won't budge!'

The Doctor studied the console. 'Reverse the polarity'.

'What?'

'Reverse the temporal polarity!'

Ruth s.n.a.t.c.hed an inspection hatch from the top of the console, extracted a circuit, reversed it, and fitted it back into place.

Immediately the whine of the apparatus began dying down. In a few moments it had stopped altogether.

The Brigadier began moving towards the connecting door. 'Is it safe to go !n there?'

Ruth shook her head. 'No, wait. . .'

'But what about that poor cheap in there?'

Ruth held up her hand for silence, studying a rapidly falling dial. 'Right, the level should be safe now.'

The Doctor and the Brigadier hurried through into the inner lab. Kneeling by the unconscious body, the Doctor lifted the loosened helmet from its head.

The face beneath the helmet was lined and wrinkled, with the pouched and sagging skin of the very old. Above it was a shock of snow-white hair.

Ruth gave a gasp of horror. 'Stuart!'

The Doctor looked curiously at her. 'Who is this man?'

'Stuart Hyde - my a.s.sistant a.s.sistant.'

'Your a.s.sistant-at his age?'

'Stuart's only twenty-five!'

'And this man's eighty or more.' The Doctor stared thoughtfully at the ancient face.

Jo Grant came hurrying in, released from her strange paralysis in the car. 'What's happening, Doctor? Were we too late?'

'On the contrary, Jo. I think we were just in time.'

It was some time later and Stuart Hyde was resting uneasily in his own little bedroom in the Inst.i.tute's residential wing. The Doctor was taking his temperature watched by Ruth Ingram, Jo Grant and the Brigadier.

'How is he?' asked the Brigadier.

The Doctor studied the thermometer for a moment and handed it back to Ruth. 'We must get him to hospital soon, but for the moment he just needs rest. He must have been a pretty tough youngster.'

Ruth sighed, remembering Stuart as he used to be, with all the vitality and bounce of an exuberant puppy. 'He was.'

'Lucky for him. Otherwise the shock of the change would have finished him off.'

'He will be all right, won't he?' asked Jo The Doctor nodded. 'He'll survive.'

'Like that?' said Ruth unhappily. 'And for how long? He's an old man!'

As usual the Brigadier was still struggling to understand what was going on. 'But what caused it? Some sort of radioactivity?'

'No, it's more than that.'

'A change in the metabolism?' suggested Jo.

The Doctor rubbed his chin. 'That's more like it, but it still can't be the whole answer.

Even if the metabolic rate had increased a hundredfold, the change in him would have taken seven or eight months, not seconds.'

The Brigadier gave up. 'Well, there's only one thing I know that makes people grow old.'

The Doctor raised an eyebrow. 'Yes?'

'Anno Domini, Doctor. The pa.s.sing of time.'

'We all know that,' said Ruth impatiently.

But the Doctor said, 'Congratulations, Brigadier. You've provided the explanation.'

'Glad to be of service, Doctor. Er - what did I say?'

'Time,' said the Doctor impressively. 'That's the answer. The only possible answer.

Stuart Hyde's own personal time was speeded up so enormously that his whole physiological life pa.s.sed by in a moment. But why? How did it happen?'

Ruth shrugged. 'The Professor might know. But he seems to have disappeared.'

Jo looked puzzled. 'What Professor?'

'Professor Thascalos. TOMt.i.t's his baby.'

'What?' yelled the Doctor indignantly. 'The arrogance of that man is beyond belief!' yelled the Doctor indignantly. 'The arrogance of that man is beyond belief!'

'Whose arrogance?' asked the Brigadier wearily. 'I do wish you wouldn't speak in riddles, Doctor.'

'A more cla.s.sical education might have helped, Brigadier, "Thascalos" is a Greek word -'

'I get it,' interrupted Jo. 'I bet "Thascalos" is the Greek for "Master".'

Stuart moaned and stirred.