"It"s our last chance gone..."

"You still haven"t taken the degeneration factor into account!" exclaimed Penley.

"But there could still be enough residual particles to form a prolonged chain reaction!" barked Clent. "Don"t you understand the risk? We could all be wiped out in an instant!"

"It"s a risk you have to take," insisted the Doctor. "If you don"t, the Base will go down under the glaciers anyway."

"Not forgetting the aliens," Penley reminded them.

There was a moment"s pause as this threat sank in. Jan had brought the Ioniser into operation once more, and it hummed quietly in the background as she came to report, "It"s on minimal power, Leader Clent," she said. "We can use it at any time you want."

Clent turned away, not wanting the others to see his fear. He knew the next step that most be taken-but he could only draw back.

"The computer said wait!" he stated vehemently.

Jan looked at him in surprise. "It said wait until we had more information. We"ve got it now!"

"Can"t you see it won"t make any difference? It dare not act- we we dare not act!" dare not act!"

"And why"s that?" asked Jamie, who had overheard Clent"s last outburst.

"Because, Jamie, the computer is faced with an insoluble problem," explained the Doctor. "Either way, the computer risks destroying itself-and that it cannot do. It can only play safe."

"But if it does nothing..." faltered Jamie, "...that"s just as bad!"

"Exactly," came Penley"s quiet voice. "Which leaves its only one course of action."

"If you think I"m going to evacuate-" Clent started to shout.

"My dear chap, you haven"t got time for that," replied Polley. "It isn"t a question of logic any more. It"s a question of world survival. You must over-ride the computer."

Clent looked at his former colleague, and shook his head. "You"re mad! You want to kill us all. There has to be another way!"

"I want to survive," rapped Penley. "And I"m willing to take the risk that your pet machine daren"t! That"s what men are for, Clent! That"s what Leaders like you are for!" He tried to appeal to the man who had once been his friend. "Be brave, Clent. Be yourself!"

"But what about the World plan? If we act too soon, it"ll be as bad as being too late! We must act at the appointed hour, and not before!"

"It"s our problem-not World Control"s!" insisted Penley.

"It"s us that"s out of step, not them-and they haven"t got aliens on their doorstep as well as the glacier! Unless we deal with them now, world civilisation is going to find itself involved in interplanetary war!"

"Someone must decide-and quickly," agreed the Doctor. He looked into Clent"s face. The Leader seemed almost incapable of words-let alone action.

"Such a decision..." muttered the Leader, then bent his head, unable to look the others in the face. "I can"t." he said.

The Doctor glanced at Miss Garrett. She shook her head and nodded towards Penley-as the Doctor hoped she would.

"It"s up to you, Penley," declared the Doctor, seriously.

The transference of authority stung Clent into one last typical act.

"I demand the right to consult the computer!" he cried, moving towards ECCO; without waiting for agreement or argument, he formally addressed the sleek head. "Problem- in addition to previous data, include the factor that the alien s.p.a.ceship is powered by an ion reactor. Dare we use the Ioniser? What are the alternatives? Answer!"

The reply shocked everyone-but Clent most of all.

Instead of its usual swift, objective appraisal and cold-blooded judgement, the tortured machine spluttered forth a stream of gibberish, half electronic, half verbal-and all totally incoherent. As its smooth head jerked from side to side in spasmodic twitches, a pungent whiff of overloaded circuits drifted from its control panel. and Clent, realising the impossible dilemma facing the machine, switched it off.

"It"s gone out of its mind!" exclaimed Jamie. "It can"t cope!"

As Clent slumped listlessly into a nearby chair, Penley took command, firmly but quietly. "Miss Garrett, inform World Control. We"re using the Ioniser now-and tell them precisely why. Full report to follow-we hope."

Victoria suddenly remembered shat the Martian warlord had said to the Doctor. A look of alarm crossed her face. The Martian s.p.a.ceship!" she exclaimed. "If you free it from the ice!"

The possibility of the Martians freely roaming the sky gripped them all with a sense of doom. What other terrifying weapons did that vehicle possess? How could they combat such a threat? It was Clent"s tired voice that supplied the answer.

"I told Varga that the Ioniser was a scientific instrument capable of melting rock," he said calmly. "But he saw it as a weapon." He paused. and studied Penley intently. "I suggest...

that it should be used as such."

For a moment, all eyes were on the two top scientists.

Each weighed the bitter consequences of his calling, and pondered upon the grim decision that he must take. Then Penley nodded, and spoke with an air of quiet purpose.

"It has to be done," he said and, moving to the Ioniser controls. began to raise its operating pitch to maximum power...

Zondal had expected the harshest of punishments for his dismal failure. With the sonic cannon wrecked and useless, and his prisoners escaped, he had knelt before Varga, only taking consolation from the fact that the finality of his punishment would at least remove the disgrace.

But defeat at the hands of the Earthlings had thrust all thoughts of a court martial out of the warlord"s mind. The most urgent need was to be ready to break free when the ice started to melt-for he was certain now that the Earthlings would use the Ioniser, whatever the risk. So Zondal had been spared. but for one propose only.

"We have to escape before the floods overcome us, Zondal!" hissed the Martian leader. "It is your task to make our engines function-quickly!"

"But the fuel cells are almost useless!" replied his reprieved lieutenant. Then. aware that if he succeeded in raising the power they needed, his earlier mistake would be cancelled out, he declared vehemently. "But I will try everything possible!"

He had tried every technical trick he knew, and other desperate experiments as well. But the most he had managed was to raise the power gauges trembling barely above the zero mark. In the cave outside, the ice groaned and shuddered in constant movements Isbur returned from a final reconnaissance outside, and closing the airlock for the last time, reported briefly. "The ice is breaking up, Commander.

The water is rising!"

Varga ordered his warriors to action stations, then moved to where Zondal was working frantically. "Do you hear, Zondal?" he demanded harshly. "But what use is freedom if we are helpless! Is there no no life in the fuel elements?" life in the fuel elements?"

"I have not given up yet!" replied the engineer, then turned, as did Varga, in response to Isbur"s sharp cry from the control room.

"Commander! Power!"

The warlord moved quickly to the control panel, followed closely by Zondal. It was true! The flickering needles were slowly rising, building towards operational level! Zondal stepped forward and grasped the controls. "The ice is our friend." He spoke in excitement. "We still have power-and it is increasing!"

"Careful, Zondal," hissed his commander. "We must time the take-off boost perfectly. There will not be a second chance!"

And as the soft hum of power began to throb through the s.p.a.ceship, Varga let his mind go forward to that moment when they would be free, in flight, and able to take a terrible revenge...

In the Ioniser control room, all eyes bar Penley"s were glued to the electronic chart showing the glacier"s advance.

His glance never left the monitor screens and power dials of the machine which his hands were controlling. Jan Garrett was feeding him the relevant information about the state of the ice.

"Glacial front reduced by seven metres-par level of ten days ago now achieved!"

"We"re winning!" exclaimed Victoria, almost hopping with excitement. But the Doctor"s face was still grim. "Not yet, Victoria," he murmured. "Not by a long chalk, I"tn afraid. It isn"t just the ice we"ve got to beat, remember."

"Instrument readings on the ice face show a continuous rise in temperature. Still short of maximum." continued Jan.

"How will we know?" asked Jamie. "Those figures can"t tell us what the Ice Warriors are up to, can they?"

Clent, standing in the background, answered Jamie"s query patiently. "The instruments on the ice face have the highest heat and shock resistance known to man," he said.

"When they cease to function, everything about them will be destroyed-including the alien s.p.a.cecraft."

"And its reactor too?" Victoria asked the Doctor.

He nodded. He didn"t trouble to remind her that their own fate was also in the balance. There"d be little enough time to worry about that if disaster did strike!

Penley, his hand poised on the power lever, took a deep breath. "Here we go," he muttered tensely. "All the way-now!"

He rammed the throttle to full.

In the midst of chaos, Varga stood, majestic and alone.

All about him, his warriors slid weakly to the floor, almost physically crushed by the combination of heat and humidity.

Only Zondal remained conscious-close to collapse, he worked desperately at the smouldering controls. His choking voice barely reached Varga through the thick yellow fumes that were filling the ship. "Must... achieve... lift-off!" were the Martian lieutenant"s final gasping words. His commander looked down at his dying comrade and spoke words that Zondal never heard.

"It was not power in our engines, Zondal," he rasped. "It was the heat! Our greatest enemy: heat-from the Earthling"s Ioniser!" Coughing from the fumes, he continued, "A magnificent weapon!" Then, still standing. he saluted his dead comrades in the Martian style. "No... surrender!" he cried as he, his ship and warriors, were blasted into infinity...

As Clent had predicted, all the seismic probe readings were dead-but the long-range seismograph print-out gave the minor blast recording that meant survival!

"Only a sub-tremor reading!" cried Jan, elated. "We"re safe! We"ve done it!"

"Miss Garrett-" responded Penley with a calm smile.

"perhaps you"d better set all circuits to automatic and tie in with World Control?"

Jan suddenly realised that several of the technicians were observing her happy outburst with amus.e.m.e.nt. With an embarra.s.sed, apologetic smile, she moved to the Ioniser controls and made the correct connections. Penley approached Clent, who was sitting at the back of the room, his head in his hands.

"Clent perhaps you"d care to check over the report we"ll need to make?"

Clent looked up, surprised. He had expected only scorn and humiliation from his colleagues. And now, of all people, it was Penley suggesting that they had a job to do-together!

For a moment, Clent"s face was blank and disbelieving. Then he smiled tiredly. "Penley-you are the most insufferably irritating and infuriating person I have ever"-he stopped in mid-sentence, and then grinned broadly-"been privileged to work with!"

Penley simply thrust out his hand to meet Clent"s, and they held the grasp for a brief moment. "Thanks, Clent..."

"Never could write a report, though, could you?" jibed the Leader gently, hiding his brief display of emotion. "Don"t worry, it"s something I"ve been trained to do."

"Without the computer?" twinkled Penley cheerfully.

"I think I can manage quite well, thank you..." declared Clent, then added-"anyway, I can always get the Doctor to help out." He turned to smile at the Doctor and his young friends-only to find they weren"t anywhere to he seen. He turned back to Penley and Miss Garrett, his face puzzled.

"That"s funny," he said. "Where on earth have they got to?"

Outside the great dome that protected Brittanicus Base, the snow had almost melted. Green shoots of long-covered gra.s.s were just beginning to show through on a messy bank that had once been a snowdrift, and which still bore the imprint of a certain heavy, blue, twentieth-century police box.

But the box itself had long since gone...