'Sounded like an all-clear.'

The noise cut out.

'What is is this place, Doctor? Some kind of research station?' this place, Doctor? Some kind of research station?'

'I don't think so, Turlough. I think it's a rather special kind of undersea military colony.'

The end of the corridor was blocked by a sliding door.

The Doctor heaved at it, but it wouldn't budge. 'Help me get this door open, Turlough, would you? Yes, an undersea colony. Armed with the sort of missiles that destroy life but leave everything else intact.'

Turlough joined him in heaving at the door. 'Photon missiles, you mean.'

'Very probably...'

The door wouldn't budge. The Doctor and Turlough looked helplessly at one another...

Tegan slipped in between them, pushed in the other direction left to right, rather than right to left and the door slid smoothly open. Tegan stepped through, and the Doctor and Turlough followed.

With the endless patience of his reptilian race, Icthar stood waiting by the ice chamber. Through the transparent door he could see clouds of mist rising about the shrouded forms. As yet there was no movement, no sign of life.

Scibus appeared. 'The Sea Base has completed a missile run. It appears that it was merely a practice.'

Icthar inclined his head. 'Then our presence remains undetected. Continue to monitor the activity of the Base.

The reactivation process should now be near completion.'

He turned to Tarpok. 'Have we any indications of conditions within the chamber?'

'No. The temperature level within is still below the range of our sensors.'

Patiently, Icthar continued his long vigil.

On the bridge, Vorshak like a good commander, was listening to the worries of his subordinates. Finally, he raised a hand, cutting short the discussion. 'We'll remain on full alert... and we'll launch another probe. For the moment, that's all we can do.'

Bulic nodded, accepting the decision. 'Very good, sir.'

He went off to supervise the launch.

The console beeped. Vorshak leaned forward. 'Bridge.'

Nilson's voice came from the intercom. 'Nilson here, Commander, in the psycho-surgery section. We have a problem with Maddox. I think you should come down.'

'Very well.' Vorshak rose and stretched, cramped after long hours in the command chair. 'Bulic, you're in command, I'll be down in the Psycho-Surgical unit.'

The Doctor and his companions had reached a storage area, filled with an a.s.sortment of drums and pressurised cylinders. Racks on the walls held pumps and nozzles and plastic hose, presumably for dispensing the various chemicals.

Tegan looked round. A store room was a store room, she thought. So far her trip into Earth's future wasn't proving very exciting. 'Doctor, what year are we in?'

'Oh, about 2084...'

'Things don't seem to have improved much since my time.'

The Doctor was wandering around, examining the drums. 'I'm afraid they haven't, Tegan. There are now just two power blocs, fingers poised to annihilate each other.'

He peered at the markings on one of the drums. 'Good grief! Hexachromite.'

Turlough frowned. 'What do they use that for?'

'It's one of the ingredients of a sealing compound for undersea structures. Harmless to humans, but in its pure state it's lethal to marine life. I thought they'd have banned it by now.'

'Progress doesn't seem to have improved things much,'

said Tegan. She led the way out of the store room.

Vorshak, Nilson and Doctor Solow stood looking down at Maddox. He was stretched unconscious on the operating couch.

Vorshak said irritably, 'Well, what's the matter with him?'

Doctor Solow's voice was grave. 'He's suffering from severe stress. I'm sorry, Commander, but it's my considered opinion that he's unfit for duty.'

Vorshak glared angrily at her. 'Unfit? He's got to be fit.

I need him. Without a synch operator this Base ceases to have any military function. We're unarmed and defenceless completely helpless!'

Nilson too looked grave, but inside he was thinking exultantly, 'Precisely, Commander. Helpless. Just as I planned!'

3.

Hunted There was a moment of silence. Both Nilson. and Doctor Solow knew that what Vorshak said was literally true. It was on this fact that their scheme depended.

Without a synch op, the Base's missile system could not function. The inclusion of a human brain in the computer-command link-up gave the Western Bloc a vital advantage in the speed of decision-making. It was also the system's weakest link.

Synch op technicians were in short supply. The training was difficult, sometimes dangerous, and only certain specially selected minds could cope. Sometimes, as in the case of Maddox, mistakes were made.

Nilson said, 'I realise Maddox's importance, Commander. You still have one option remaining though I almost hesitate to mention it.'

'And that is?'

'You could release the duplicate programme disc. Then Doctor Solow could probe deeper into Maddox's mind, break through the barriers and rea.s.sure him.'

Vorshak frowned. Synch-op programming was a closely guarded military secret. As far as was known, the Eastern Bloc had not yet achieved it, though they were certainly working on the problem. 'I can't do that. Not without authority from HQ and I can't ask for authority because we're forbidden to break radio silence while the emergency lasts.'

'If we're to maintain operational efficiency, Commander, it's the only way.'

Vorshak hesitated. To release the duplicate programme disc without proper authority could endanger his career but to leave the entire base unarmed and helpless would endanger hundreds of lives.

Doctor Solow said gently, 'I'll take full responsibility, sir. There are humanitarian as well as military considerations involved. Unless Maddox is re-programmed, he'll have a total mental collapse.'

Her intervention tipped the balance. Vorshak crossed to a wall-safe, took an entry-coder from his pocket and punched out a complicated access code. The safe-door slid open. Vorshak removed a gleaming metallic disc and handed it to Nilson.

'Don't let it out of your sight. If it gets into enemy hands '

'I'll return it as soon as the re-programming is finished,'

promised Nilson.

Vorshak nodded and left the PS unit unaware that the precious disc was in enemy hands already.

Nilson studied the disc exultantly. It represented a valuable espionage coup in itself, though for the moment there was no way to get the information it contained off the Base. More important, it would give Doctor Solow and Nilson total command over the mind of Maddox and enable them to proceed to the next stage of their plan.

Carefully Nilson inserted the disc into the psycho-surgical console.

Doctor Solow was already moving aside the little flaps of artificial skin and hair that covered the synch terminals in Maddox's head. She plugged in the two leads that ran from the console and stood back. Nilson touched the control and the programme began to run.

Maddox stirred and moaned, then relaxed. Nilson studied him uneasily. 'You're sure this will work?'

Doctor Solow checked the connections to Maddox's head. 'That programme feeds information straight into the deepest control centres of Maddox's brain. Soon we can cut into that programming, alter it. Whatever commands we give him, Maddox will have no other choice than to obey.'

The Doctor's little group had left the chemical store and was trudging along more endless white metal corridors.

Tegan was fed up with it. 'Have you any any idea where we're going, Doctor?' idea where we're going, Doctor?'

'As a matter of fact, I do, Tegan. We're making for the Bridge. Repairs to the TARDIS will take a little time. If we have to stay here for a while, we'd better get the Captain's permission.' They came to a lift. 'Aha!' said the Doctor.

Turlough studied the control panel. 'Up or down?'

'Well, if I remember correctly, the Base command centre is usually at the top of the structure.'

Before the Doctor could stop him, Turlough reached out and stabbed a control b.u.t.ton on the panel.

Immediately a light began flas.h.i.+ng on the control panel.

The Doctor sighed. 'Really, Turlough! You see what you've done?'

'I only pressed for the lift. What's the matter?'

The Doctor indicated the light. ' This This is. There's obviously some kind of a code, so they can detect unauthorised users. It's what's called security. We'd better find someone in authority, and quickly. Come on.' is. There's obviously some kind of a code, so they can detect unauthorised users. It's what's called security. We'd better find someone in authority, and quickly. Come on.'

A door slid across the corridor ahead of them, blocking their path.

'What do we do now?' asked Tegan.

'They've sealed off the area. We'd better get back to the TARDIS. We'll be safer there.'

Hurriedly the Doctor led them back along the corridor.

They were in a military-style establishment, a closed environment whose inhabitants were almost certainly under considerable pressure. In such an environment, the security guards were more than likely to be trigger-happy.

Vorshak was back on the Bridge, where the atmosphere was still very tense. Recent mysterious events, combined with the practice missile-run, had left everyone edgy.

'Perimeter defence now complete, Commander,'

reported Preston. She stared at her monitor screen and then exclaimed, 'Intruders, Commander! Security has detected intruders on the Base.'

'What? Where are they?'

'Area C, Commander.'

Vorshak's first thought was for the duplicate programme-disc. 'Post guards around the PS unit. Tell Controller Nilson and Doctor Solow what's happened. Any sign of an intruder and they're to destroy the programme disc immediately. Send combat teams into the area to hunt down the intruders.'

Preston moved over to a security intercom, and began issuing urgent commands. 'Battle teams eight and ten proceed to area C immediately. Suspected intruders. Team seven to PS unit...'

Vorshak turned to Bulic. 'What do you think?'

'An unidentified object, the destruction of the probe and now this. Too much for coincidence.'

'I agree. We must act quickly. You and Preston take command of the combat teams. Get them moving.'

'Right, sir. Preston, come with me.' Bulic and Preston hurried from the Bridge.

In the PS unit, Nilson spoke into the intercom. 'Message acknowledged. We'll remain alert.'

Doctor Solow was hovering over the unconscious Maddox. 'What was all that about?'

'Some kind of security alert intruders. We'd better hurry.'

'I've almost finished...' She waited a moment or two longer, and then removed the terminal leads from Maddox's skull, replacing the concealing patches of skin and hair. She touched another control. The upper portion of the operating couch tilted slowly upwards, until Maddox was sitting upright.

'How do you feel, Maddox?' asked Nilson gently.

Maddox opened his eyes and stared vaguely at him.