'You can walk out of here now,' suggested the Doctor.

'You'd be safe-even if your s.p.a.cecraft was was destroyed.' destroyed.'

'But without this vehicle,' whispered the grim-faced warlord, 'we cannot return to our planet.'

The Doctor was about to inform the Ice Warrior that his distant home planet-Mars-had long since died, when he stopped himself, horrified. With nowhere to return to, the Martians would be forced to stay-but it wasn't in their nature to remain guests for long. They were conquerors, colonisers and invaders; and with their deadly weapons, probably invincible! Suddenly, the Doctor thought of a vital question.

'Why did you come here in the first place? What was your mission, Varga. Tell me!'

'To investigate this planet... and report,' answered Varga. His next words confirmed the Doctor's worst suspicions. 'We find that we are... superior.'

The Doctor's mind seethed with alarm. This small squad of Ice Warriors, with or without their s.p.a.ce vehicle, could devastate and dominate Earth-continent by continent-if they chose to! And he had a definite feeling that this would have been part of that original Martian plan, conceived so many centuries ago, and halted only by a freak landing on that prehistoric glacier. Suppose there were other scout ships, buried in the ice? Varga mustn't be given the chance to put his secret orders into practice-which meant there was only one way out, dreadful but necessary. He began speaking with what seemed an unnecessary loudness-but not for Victoria's benefit. Clent had to be persuaded to act-and act now!

'You do realise,' stated the Doctor emphatically, 'that at a certain point almost immediately, fact-my Base will have to activate the Ioniser regardless of the consequences regardless of the consequences?'

Zondal didn't catch the urgent emphasis. He sneered in disbelief. 'And risk destroying you-and themselves? They are not fools!'

'Better that.' the Doctor started to say, 'than-'

In a flash, Varga's fist had grabbed his arm, exposed the tiny communicator and wrenched the device free, switching it off in the process. He examined it closely, then laughed.

'A communicator! How useful!'

The Doctor had always known the risk of discovery.

Realising what he had been trying to do, Victoria gasped in fear of Varga's retaliation. Neither of them expected his response.

'When the time is right,' hissed the warlord arrogantly, 'we will use this device ourselves.' He stepped closer to the Doctor.

'You have been most helpful, Doctor. You will forgive interruption of your warning to your friends. Shall I complete it for you?' He laughed cruelly. ' Better that than... be conquered Better that than... be conquered by these Martians! by these Martians! And you are right!' He gestured towards the engine complex, and his next words struck fear into both the Doctor and Victoria. And you are right!' He gestured towards the engine complex, and his next words struck fear into both the Doctor and Victoria.

'There is one thing we need to complete our power,'

hissed the Martian arrogantly. 'Then we shall be invincible- and this planet will be ours to conquer as we please!'

8.

The Martian Ultimatum Leader Clent stared at the blank video screen and said nothing for several seconds. It seemed that with the Doctor's message ending so abruptly-their last chance had vanished.

'What can we do?' asked Jan. 'The Doctor! We've got to help him!'

Clent shook his head. 'You heard what he said.

Regardless of the consequences, he wants us to take the risk and use the Ioniser.' He frowned. 'But he's not only offering himself as a sacrifice-it's us as well!'

'If only he could have said more... Perhaps he means the s.p.a.ceship's reactor isn't isn't dangerous?' dangerous?'

'But the aliens are are...' replied the Leader grimly. 'It's no good guessing, Miss Garrett. We must have facts!'

She had to agree. 'Until we programme the computer with the correct information, it cannot instruct us how to act.'

Clent turned back to the Ioniser monitors. They were stable, but almost dormant at half power. 'If only the Ioniser would hold...'

'At present output, it's steadily losing ground to the glacier.' Inside her mind, a silent voice shouted Jan's real opinions. Forget the glacier! Do something to save the Doctor and the girl! We owe them that much! We cannot let them die! Aloud she said, 'We dare not increase power... not yet.'

Clent turned to her. She sensed the deep confusion in his mind. He was torn between duty, humanity and the need for action-knowing that whatever decision he took, the result could spell disaster... Suddenly, the computer hummed into life.

' World Director, Ionisation Programme. to all sectors. The new World Director, Ionisation Programme. to all sectors. The new control equation originating from Brittanicus Base will be adapted to control equation originating from Brittanicus Base will be adapted to conditions prevailing each sector, and linked to World Central conditions prevailing each sector, and linked to World Central Control. On central command pulse, a concerted intercontinental Control. On central command pulse, a concerted intercontinental attack on the glaciers will commence in six hours exactly. Report attack on the glaciers will commence in six hours exactly. Report readiness in three hours. Leaders to confirm status report one hour to readiness in three hours. Leaders to confirm status report one hour to zero. Message ends. zero. Message ends. ' '

Jan tanned desperately to Clem. 'We can't do it!' she cried hopelessly.

Clent's face was stern; like a soldier taking orders in the face of imminent destruction, he knew instinctively that he must act without question. 'If we don't act, the world plan must fail! We have no choice, Miss Garrett!'

Jan was too well trained to defy her superior, but she clutched desperately at one last straw... 'The computer must must be told,' she insisted firmly, 'as a matter of procedure.' As Clent started to protest, she added quickly, 'With the fresh directive from World Control, it may be able to resolve our local situation.' She was relying desperately on Clent's addiction to the rule book and, to her relief, he nodded in reluctant agreement. be told,' she insisted firmly, 'as a matter of procedure.' As Clent started to protest, she added quickly, 'With the fresh directive from World Control, it may be able to resolve our local situation.' She was relying desperately on Clent's addiction to the rule book and, to her relief, he nodded in reluctant agreement.

'Very well, Miss Garrett, feed the relevant data to ECCO, if you must.' But at the back of his mind he instinctively knew what the computer would say in answer to the grim dilemma. There was only one reply it could give- and that answer would save no one. Seconds later it gave its response.

' As instructed, set up all circuits to the new equation. No action As instructed, set up all circuits to the new equation. No action to be taken until further data available regarding potential nuclear to be taken until further data available regarding potential nuclear explosion. Prepare to notify World Control in event of unresolved explosion. Prepare to notify World Control in event of unresolved emergency. Repeat, take no action! emergency. Repeat, take no action! ' The machine fell silent. ' The machine fell silent.

Clent looked across at Jan. 'It's what we both expected, isn't it,' he commented wearily. 'But the computer must be obeyed. We must wait.'

'In five hours from now, you have to report that we are in emergency status!' exclaimed Jan. At least we have that at much time!'

Clent studied her tense face, and saw she didn't understand. 'Miss Garrett, you still don't realise the logic of the computer's decision not to act, do you?'

Puzzled, she shook her head. 'The computer can only ever be logical. It hasn't enough facts-it told us so a moment ago.'

Clent's reply carried an undertone of despair. 'We have just asked the computer if it is prepared to commit suicide. If we use the Ioniser and we explode the alien reactor, the Base-and the computer-will be destroyed. If we do not use the Ioniser, the glaciers will advance and destroy the Base.

Either way, its survival is at risk-and one of its prime directives, programmed as a vital part of its basic circuitry, is to survive! Now do you see the dilemma?'

Jan was silent. It wasn't only the computer's dilemma, she realised; it was Clent's as well. Whatever he did, failure was staring him in the face.

'We can at least evacuate,' she said quietly, knowing what his reaction would be. 'There's still time...' Clent was shocked, and angry. 'Retreat? Throw in the towel? Perhaps you would be happy to face world opinion afterwards, Miss Garrett. I would not!'

'Is that all that matters? It isn't only your reputation at stake. There are the lives of-'

Jan stopped in mid-sentence as the picture of Walters flashed on to the video screen. His brisk message startled both Jan and Clent into action.

'Security to Leader Clent. Two emergency arrivals, sir.

I've had them both brought to the medicare centre for treatment. One of them's Scientist Penley!'

Zondal was supervising the removal of the sonic cannon from its usual mounting inside the s.p.a.ceship to a traction unit in the cave outside. Varga turned to the Doctor.

'As you can see, Doctor, we have more than just personal destructors!' He pointed to the weapon on his arm, and Victoria shuddered, remembering vividly the horror of that deadly gun. 'This can destroy a man in an instant-but the sonic cannon is capable of wiping out whole cities!'

'What's it to be used for?' asked the Doctor.

'It is an ultimatum,' hissed Varga. He laughed brutally.

'An ultimatum that accepts only one kind of reply-an agreement!'

'But why?' asked Victoria bravely. 'You've already got us as hostages!'

'Yes.' agreed the Doctor. 'What else do you want?'

'Information,' said Varga. 'You have asked enough questions. Now you will provide answers..?'

'I've already told you all I know about the Ioniser,'

replied the Doctor. 'You don't need to worry-'

'What is its power source then? Tell me that!'

Suddenly the Doctor saw the situation in all its clarity.

While he had been desperate to know what sort of reactor the Martians had on their s.p.a.ce craft, they had realised that the Base aright be the source of vital fuel for their reactor! The truth was, they were as helpless as Clent and the scientists-

the perfect stalemate. But a distant groaning from the glacier outside reminded him of that one random factor. The moving river of ice was dependent on no one; unless it was stopped soon, the Ioniser Base would be swept away like every other man-made object in the glacier's path.

'So that's what you need...' he said shrewdly, looking past Varga into the engine complex. 'Fuel-for your reactor.

Without it, you'll never be able to break free! '

'Answer my question!' commanded the warlord, holding his sonic destructor close to Victoria's head, 'or the girl dies!

Quickly!'

'And if I tell you?'

'We will take what we need, and use it to blast our way out of the glacier!' came the fierce reply. 'Speak!-'

The Doctor looked suitably dejected. He turned from the engine complex to face Varga. 'Mercury isotopes-is that it?'

'You have them?' demanded the warlord eagerly.

Victoria's face filled with dismay at the Doctor's surrender to the Martian demands. 'Doctor, you shouldn't have told him!'

'You're more important, Victoria,' murmured the Doctor, then spoke to Varga defiantly. 'You won't find Leader Clent so easy to persuade! He's got a will as hard as granite!'

'The sonic cannon,' whispered Varga, 'can be programmed to disintegrate the hardest rock. This man will do as we ask-or we will smash his installation to pieces!' He pointed through the open doorway of the airlock.

There, at the entrance to the ice cave, pointing out over the hillside towards the Base, stood the sonic cannon. At Varga's gesture, Zondal stepped forward to the control panel inside the main complex of the s.p.a.ceship. A video-radar screen, with a fire-path already plotted, was suspended over the gun controls.

'The weapon has only to be primed, and fired at my command,' hissed the warlord. 'Zondal is an expert bombardier. Let us hope he does not have to demonstrate his skills more than once!'

When Clent and Miss Garrett arrived in the medicare centre, Jamie was already encased in the computerised diagnostic chamber. Penley, who was overseeing its purring function, didn't seem to hear Clent enter.

But when he did turn round to acknowledge the Leader's sour greeting, his expression was one of deep relief.

'So you've come back!' commented Clent.

'Of my own free will,' replied the renegade scientist.

'Largely because I was talked into it by that chap the Doctor- and this young friend of his.'

'Is that all you expect?' jibed Clent. 'Free medical treatment? Don't think you'll be reinstated! You're an outsider-self-declared!'

Jan was examining Jamie. 'What's wrong with him?' she asked Penley anxiously. He smiled in reply, appreciating that she didn't share Clent's anger.

'He was shot by the warriors' guns,' Penley answered soberly, 'when they killed Arden. I was afraid there'd be some neural damage, but the diagnosis says it'll only be temporary-given the right treatment,' he added challengingly. 'Or will you try and put a stop to that, too?'

Walters, hovering in the background, looked uneasy. All the signs pointed to yet another row between the two scientists. Clent gestured Walters to remain.

'Stay here, Walters,' he ordered, 'you may be needed.'