Suddenly the junction box in the corridor exploded.

The console blew up and the coil disintegrated in a shower of sparks.

The Machine disappeared.

Two Prison officers, newly restored to freedom and authority were walking along the corridor, enjoying things being more or less back to normal.

They stopped in astonishment at the sight of the exploded, still-smoking junction box.

Suddenly the Machine materialised in front of them, throbbing hungrily.

A blood-red shimmering filled the air as it sucked the life force from them in one fearful surge of power.

The Doctor was still muttering calculations as Jo came back into the Governor's office with a tray on which was a bowl of tomato soup.

'Here you are, Barnham, some nice hot soup for you,'

she said encouragingly. 'Eat it all up.'

Barnham took the soup. 'Thank you, miss.' Obediently he began to eat.

'That's it,' said the Doctor suddenly. 'I think that might just do it!'

He jumped to his feet and dashed out.

As always, Jo's insatiable curiosity got the better of her.

'Wait for me, Doctor,' she called and ran out after him.

Barnham looked on in mild astonishment.

Benton's phone rang. 'Sergeant, sorry, Acting Governor Benton.'

'It's Doctor Summers here. I was wondering if those extra medical supplies had arrived?'

'Medical supplies? Hang on, Doctor Summers, I'll check.'

Benton began sorting through the file of receipts and requisitions on his desk.

Suddenly he became aware of Barnham hovering over him. 'What do you think you're doing mate?'

'Doctor Summers,' said Barnham happily.

'You what?'

'I'd like to talk to Doctor Summers.'

Benton found the paper he was looking for. 'You go and talk to whoever you like mate,' he said absently. He picked up the phone. 'Doctor Summers? They're here all right.

Should be on their way over to you now.'

By the time Benton had finished his conversation and put the phone down Barnham had wandered off.

Jo and the Doctor looked down at the exploded junction box and the two crumpled bodies.

'Oh no!' whispered the Doctor. 'That thing's escaped again.'

'But how?'

'It must have stored up all its energy until it had enough power to fuse the circuits.'

Which meant that it would be hungry again, thought the Doctor. He got up and walked slowly towards the Process Chamber, as if dreading what he might find.

'Be careful, Doctor,' called Jo and hurried after him.

They stood in the doorway of the Process Chamber, looking round in horror at the wrecked room. The place was a total shambles, smashed furniture and shattered equipment scattered everywhere.

'What happened?' whispered Jo.

'It's stronger than ever now, Jo. How on earth am I going to stop it?'

Barnham came wandering along the corridor.

He stopped for a moment staring in distress at the two bodies. Then, as if drawn by some compulsion, he made his way towards the Process Chamber.

'Will you be able to set up that thing with the coils again?'

asked Jo.

The Doctor shook his head despairingly. 'No, that would never work twice. The thing's too intelligent. It would probably kill me before I got near it.'

Suddenly they heard the familiar throbbing noise and the Keller Machine materialised on the table before them.

They could feel its pull now, and Jo in particular seemed transfixed. She began taking stumbling steps towards the box.

The Doctor tried to pull her back, and found to his horror that he couldn't move. The mind parasite had become too strong for him.

Jo stumbled nearer the Machine...

15.

The Mind of Evil Suddenly the throbbing of the Machine died down.

The Doctor pulled Jo back and Barnham stumbled into the room.

'Get back, Barnham,' shouted the Doctor. 'Don't come in!'

Barnham stared dazedly at him, and came on into the room. 'I had to come... then I heard this noise.'

As he came closer, the throbbing of the Machine died down completely.

'It's stopped,' whispered Jo.

Barnham looked round the room. 'I remember this place. Something happened to me here. Something terrible.'

Frightened, Barnham backed away and as he retreated towards the door, the terrible throbbing began again.

A wonderful, incredible idea came to the Doctor's mind.

'Barnham, don't don't go,' he called. go,' he called.

Frightened Barnham still backed away.

The throbbing grew louder.

'Barnham, it's all right!' called the Doctor. 'Come back here, please. It can't hurt you and while you're here it can't and while you're here it can't hurt us! hurt us! ' '

Barnham advanced slowly into the room. The throbbing of the Machine died away again.

The Doctor took Barnham's arm. 'That's right, this way.' He picked up an overturned chair, set it up close to the Machine and sat Barnham down on it. 'That's right, old chap, you sit there.'

Jo saw that Barnham was right next to the Machine and the Machine was silent, dead.

'I don't understand, Doctor. Why?'

The Doctor was overjoyed. 'Eureka! Don't you see, Jo, the Mind of Evil. The creature in the box feeds feeds on the evil pulses in the mind.' on the evil pulses in the mind.'

'And Barnham doesn't have any!'

'Exactly! The Machine extracted them all. Now, somehow or other the effect of Barnham's mind acts as a screen, it neutralises the mind parasite. As long as Barnham's here, we're safe!'

Captain Yates and Major Cosgrove rose, as the Brigadier strode briskly into the Mobile HQ.

'Good afternoon, Major Cosgrove. How are you, Captain Yates?'

Mike Yates had had a chance to clean himself up, and he had undergone the attention of a UNIT medical orderly. His right arm was in a sling but otherwise he was pretty much himself again.

'Recovering rapidly, sir,' he said cheerfully.

'Good. Well sit down both of you. How's it going, Major?'

'Fine sir and there's excellent news. I've checked with the Ministry of Defence and it appears that Thunderbolt is equipped with an abort mechanism. As soon as it's in go condition we can blow it up any time.'

The Brigadier said happily, 'So, if the Master threatens to launch the missile we simply blow it up from here?'

'Exactly, sir.'

The Doctor had taken the dome from the top of the Machine and he and Jo were looking in horror at the creature beneath. Not that it was all that impressive. It was a lump of blue, spongy substance, not unlike a brain itself in appearance, with a sort of central nucleus that just might have been an eye. Yet somehow it radiated evil.

'Can't you kill it now, Doctor?' asked Jo.

'The creature is incredibly resilient. It would take an atomic explosion to destroy it completely. Or an enormous charge of electricity. Yes, that's it!' The Doctor made for the door. 'You and Barnham wait here. I've got to go and see Sergeant Benton.'

Jo shuddered, but said bravely, 'All right.'

The Doctor put a hand on Barnham's shoulder.

'Barnham, old chap, listen to me. Will you stay here with Jo till I get back? It's important.'

'I'm frightened,' said Barnham piteously. 'It's evil.'

'I'll be as quick as I can,' said the Doctor. 'Look after him, Jo.'

The Doctor hurried away.

Jo smiled encouragingly at Barnham, trying to distract him from the horror in the Machine.

'What's your first name?' she asked. 'I don't think you ever told me..

The Doctor was showering a baffled Benton with orders and instructions. 'Now you're sure you've got all that, Sergeant?'

'I think so, Doctor. Extra heavy-duty cable, arrangements with the National Electricity Grid for a ma.s.sive power surge on command. I'll get on to it right away.'

'Please do,' urged the Doctor. 'It's all very urgent.'

'It's going to take quite a bit of organising...'

'I don't doubt it,' said the Doctor impatiently.

'Nevertheless, please do your best.'

Benton reached for his telephone but it rang as he put his hand on it. He picked it up. 'Acting Governor Benton.'

A deep, puzzled voice said, 'I beg beg your pardon?' your pardon?'

'This is Stangmoor Prison. Acting Governor Benton speaking.'