"That wasn"t planned!" protested Clent. "He wasn"t going to harm you-it was the computer that he wanted to smash!"

"I do not need your explanations," responded Varga.

"Our truce is at an end!" As the Martian strode into the control complex and began studying its equipment and layout, Jan had the distinct feeling that the truce was never intended to be kept. This alien was ruthless; unless they were careful, Walters would not be the last to die. She motioned to the few remaining technical operators to do nothing to antagonise the Martians. One glance showed her that they were not likely to make even a token resistance.

"What is it you want?" Jan boldy asked.

Varga looked at her arrogantly. "I have one major need; mercury isotopes for my s.p.a.ceship"s reactor. You will give them to me."

Clent frowned, and intervened cautiously. "But... we don"t use mercury isotopes."

"The Doctor stated that you had what we need-here!

Do not try to trick me!"

"He was wrong-we have one," answered Clent simply.

"What good would lying do?"

The warlord glowered at Clent, then moved towards Jan. He spoke gently, but the menace in his voice was unmistakable.

"Tell me," he whispered smoothly, "what will hap-pen if we shut off your reactor in order to extract the fuel elements that we need?"

"You can"t do that!" Jan answered in alarm. "It powers everything: heat, light-"

"And the Ioniser..." hissed the Martian. "Without the reactor, you would be completely at the mercy of the glacier."

"You don"t realise the dangers!" Clent exclaimed, his face pale with stress. "The power source is locked in directly with the Ioniser. If you cut out the energy pulse before it reduces to safety level, the feed-back effect will blast you and this building into a state of ion-flux!"

The warlord studied him briefly, then moved across to examine the Ioniser control panel. "What is its temperature range?" he hissed, his great fists poised above the controls.

"Don"t touch it!" cried Clent. It"s fully primed!" Varga"s hand fell back, but his arrogant head turned towards Clent, waiting for the answer. "It can melt rock; muttered Clent reluctantly.

"It can volatise rock!" the Martian was obviously impressed. "What a weapon!"

"It isn"t a weapon!" insisted Clent nervously. "It"s a scientific instrument!"

"But highly dangerous," interjected Jan. "unless it"s handled correctly. You do so at your own risk," she added.

"You are its operator?" hissed Varga, then taking her nod of a.s.sent as answer, continued, "You will take it down to safety level. Now!"

Jan looked towards Clem. His shoulders slumped; he nodded wearily in agreement. But Jan hadn"t given in completely yet. "It"ll take some time," she said.

"Do not attempt to trick me," rasped the Martian. "I know that you are afraid its heat will explode my ship. If you make one false move..." he placed his sonic destructor at Jan"s head "... you will be the first to die!"

Clent stepped forward to defend Jan. Varga"s gun swung in his direction. He strove to hide his fear. "Miss Garrett is the only person who is qualified to disconnect the Ioniser safely! If you kill her-"

Varga moved closer to the Leader. "And what exactly do you do here?" he asked softly. A little of Clent"s old dignity returned. "I am in charge of this establishment, with the official rank of Leader."

The Martian coughed out his menacing laugh, and placed the sonic weapon at Clent"s ear. "Then you have less value to me than your colleague, who has more valuable skills." The warlord looked at Jan, her eyes showed her fear.

"To kill this man, your Leader," he hissed, "would be no loss to me. Do you wish to see him die?"

"No!" cried Jan. "Please!"

"Then do as I say! Close down the machine as quickly as is safely possible!" Varga brutally thrust the sonic weapon against Clent"s cheek, making him howl with pain. "Or your Leader will be destroyed!"

Zondal had been so effected by the toxic gas that he was likely, to remain in a deep coma for hours. Victoria kept glancing at the sprawled, ma.s.sive body nervously-but the Doctor was wholly concentrating on adapting the intricate mechanism of the sonic cannon"s control panel to a purpose all his own.

"But what is it you"re trying to do?" asked Victoria.

"It"s a bit difficult to explain, Victoria," replied the Doctor, without pausing. "You see, this weapon works on the basis that sound waves cause the objects in their path to reverberate."

"The objects vibrate in sympathy," nodded Victoria. "I know. Father told me about it once."

The Doctor frowned at a particularly involved piece of circuitry, then carried on. "Well, if you can produce an un un sympathetic vibration, severe damage results..." sympathetic vibration, severe damage results..."

"Damage?" asked Victoria, then added brightly, "Like when a singer hits a note that breaks gla.s.s?"

"That"s it-only the Ice Warriors make it happen to the neural and cell systems of the human body. My plan is to change the frequency of this gun"s pulse rate so that it affects the Martians, and not us-to frequency seven, I think."

"Frequency seven? What will that do?"

"Primarily, it affects liquids. And I"ve got a theory that the Martians" cells contain a much larger fluid content than ours." He stood back, apparently satisfied, then rubbed his chin thoughtfully.

"But you"re not sure." Her eyes widened in alarm.

The Doctor nodded soberly. "There are bound to be side-effects," he agreed, "but the warriors should get the worst of it. You see, their helmets will trap and intensify the sound waves-in fact I"m banking on that!"

"You mean it"ll knock the Martians out," asked Victoria tentatively, "but just leave the scientists a bit dizzy?"

The Doctor carefully replaced the casing of the control panel. Victoria could tell from his face and the hesitation in his reply that he wasn"t at all happy. "Or can something go wrong?" she demanded.

He looked her straight in the eyes, and gave her an honest answer. "Human brain cells also contain a high percentage of liquid. Unless I"m very careful, the effect on our friends could be fatal."

Jan stepped back from the Ioniser controls, her face bitter with defeat. "It"s done-operating at minimal status."

She looked at Clent-but found no response there. It was as though he was in a world of his own. "The ice is already advancing." She pointed to the chart. Varga wasn"t interested in the glacier.

"Disconnect the machine totally!" he barked.

With no alternative but to do as he commanded. Jan opened the power connector and the machine died. Its pitch sank to a feeble drone.

"Now the reactor!" ordered the warlord.

"Not until all residual power has drained off!" replied Jan sternly. "You know the danger!"

"You will regret this, Varga." Clent declared, strangely calm. "You cannot fight the whole world"

"Your world is nothing"" hissed Varga contemptuously.

"We will live to regret only that my superiors on Mars cannot congratulate us." He gestured abruptly towards Jan. "Hurry!"

All eyes, Martian and human, were on the dying machine. No one noticed the ragged form that had hidden so skilfully in the shadows outside the doorway to the control room, and who watched with dismay the fateful situation in which Clent and Jan were trapped. Penley had woken from the effects of the tranquilliser gun to find himself strapped down to the trolley in the medicare laboratory. It had been minutes before he realised that whoever had fastened the restrainers had left them cunningly half-caught. It had been an easy task to unloose them and set himself free. Jame, coc.o.o.ned within the healing confines of the diagnostic unit, was unconscious but seemed, Penley noted, to be improving rapidly.

But Clent was a different matter-somehow, he had to be made to see that what he was doing could only end in disaster. It wasn"t until Penley reached the vestibule outside the control room and realised just how desperate the situation was, that he felt a genuine respect for Clent"s courage. It would have broken a lesser man. Faced with not only death but the destruction of all he held to be of importance in his scientific career, the Leader remained quietly defiant... and utterly helpless.

But so am I, thought Penley to himself. These Martians seemed invincible! Silently, he drew back into the shadowed corner to think-and in doing so, jarred his shoulder against a control box. Irritated. he glared at the unit-then looked again, wild thoughts racing through his mind. It was an air-conditioning stabiliser. At present set on automatic, with preset limits, it could also be converted to manual. His mouth dry, Penley"s fingers fumbled rapidly to open up the casing; his mind swiftly a.s.sessed what he knew about the Martians. It was the boldly labelled status gauges that had triggered his thoughts: temperature, oxygen ratio, and humidity. These aliens were entirely at home in such Ice Age conditions as might exist on certain parts of their home planet, Afars. Well, thought Penley, we"ll soon put an end to that! Switching the controls to manual, he increased all three elements to maximum-and prayed.

The effect was almost instantaneous. Rintan, the warrior standing closest to an air-conditioning grille in the control room, started to reel. The floor was rising and falling beneath him like a sinking ship! His great fists clawed at his throat, and his usually softly wheezing breath changed to a series of great tearing sobs. Within seconds, the humans. too, felt the increased surge of toxic heat-but still threatened by the waariors" weapons, they looked on helplessly as each of the Martians struggled to remain conscious. Only Varga kept any degree of keen awareness. He whirled to confront Clent furiously.

"What have you done to us!" he snarled, "You have tricked us! For that you will die!"

But even as he raised his gun, a new terror struck. An immense, pulsing throb of sound filled the room-and its effect on the Martians was even more astounding than that of the heat. The humans slumped lifeless to the floor, like stones.

The effect on the Martians was more terrifying. The sound flooded over them, through them-but, worst of all, it seemed to penetrate their great helmets. Crying out hoa.r.s.ely, lurching in agony, there was no escape from the relentless sound that threatened to crush their very brains... Then, just as suddenly, the sonic terror ended.

But the combined effect of the sound and the atmospheric a.s.sault-which still hadn"t stopped-had left the warriors. Varga included, in a state of confusion and shock...

Then, even as they still recovered, the voice of the Doctor came through on Varga"s personal communicator.

"Varga! This is the Doctor. Will you retreat-or shall I use frequency seven again?"

Nearly out of his mind with pain and anger, Varga still registered that deadly number: Frequency Seven. Used in the prisons of his home planet as a form of aversion punishment, continuous doses of it could destroy the brain, leaving the body a living vegetable. How did the Doctor know this?

"Varga!" came that relentless voice once more, "Answer- or I fire again!"

There was no other choice but to obey. With a furious, sweeping gesture, the warlord ordered his warriors from the building. Furious, Varga shouted aloud the message to the Doctor: "You will suffer for this!" Then, lurching past the crumpled body of the human in the vestibule outside, the Ice Warriors streamed out into the freedom of the snowy wastes-and the protection of their s.p.a.ceship.

But when they reached the ice cavern, they discovered the sonic cannon fused and destroyed, Zondal unconscious, and both their prisoners gone...

10.

On the Brink of Destruction!

Jamie, who had just recovered consciousness, was helped out of the snug confines of the diagnostic unit by an almost hysterically relieved Victoria. The Doctor had gone on ahead to the control room without explanations. He had told the two youngsters to follow as soon as possible.

"What"s been happening?" asked Jamie, stretching his cramped limbs. Then, as memories crowded back, he looked at Victoria more thoughtfully. "Arden-is he-?"

She nodded quickly. Then, as they walked through the empty corridors to the control room, she filled in what had happened during Jamie"s healing sleep, and what they might expect to find. On arrival, the Doctor quickly made it clear that there was no time for questions or answers. As he helped Penley to his feet, he indicated the reviving bodies of the scientists and technicians who were littered all over the control room floor.

"We"ve no time to waste. Help some of the others, will you?"

"That was rather a neat trick," commented Penley. "How did you do it?"

The Doctor smiled, mildly apologetic. "Made a mess of the Ice Warriors" weapon system, I"m afraid. I"ll tell you about it another time."

Jan, quickly recovering, turned to the Doctor in dismay.

"The Ioniser-they made me disconnect it!"

"Then link it up again-fast as you can!"

Jan looked to Clent for confirmation.

"That"ll be perfectly in line with the computer"s directive, Miss Garrett. You may proceed." Jan hurried to put his order into action. Clent turned to the Doctor, his tired face filled with relief. "Thank you, Doctor," he said, and then. seeing Penley standing at the Doctor"s shoulder, frowned. "You played your part well. I gather," he conceded. But his eyes still looked unfriendly.

"Clent"-the Doctor interjected urgently-"the s.p.a.ceship"s reactor is ion-powered. Mercury isotopes-"

The Leader"s face fell. One of the main reasons why the Base reactor didn"t use mercury isotopes was that their critical fusion level had proved uncontrollable on a large scale. "Then we dare not use the Ioniser at full force," he said dejectedly.