Nyssa and Tegan stared helplessly at the Doctor's ashen face. Then Tegan suddenly caught a glimpse of something she recognised glinting between the Doctor's fingers. Instantly she shoulder-charged the towering Cyberleader with all her strength.
Her slight frame bounced off his gigantic bulk like a pingpong ball, but the Cyberleader was distracted just long enough for the Doctor to leap forward and manoeuvre himself round behind the cumbersome figure. Flinging both arms around the Cyberleader's thick body, he was able to scrape the gold edge of Adric's badge rapidly up and down the serrated grille covering the ventilator unit on the automaton's chest.
Immediately the precious but deadly grains were sucked into the unit. Nyssa and Tegan dived for cover beneath the console as the Leader's blaster fired erratically
in all directions as he swung violently from side to side in a vain attempt to throw the Doctor off. The Doctor cried out in agony as the Leader trapped his forearms between metal elbows and armoured sides. But still he rubbed the badge as hard as he could against the grille, and more and more gold filings were sucked into the ventilator.
Gradually the Cyberleader began to emit a desperate choking sound and sticky black bubbles started frothing out of the grille. Tegan threw herself in a kind of rugger tackle at the monster's legs and clung on for dear life as the thing staggered wildly about, whipping viciously to and fro and firing the blaster haphazardly at the console and the walls of the chamber as it struggled to maintain its balance.
Eventually the Cyberleader's movements became more and more sluggish and his cries more and more like the sound of a human being fighting for breath. Finally he slumped forward and the Doctor took his chance to grab the blaster from the Cyberleader's weakening grasp. Yelling to Tegan to let go of the legs, the Doctor thrust the weapon against the Cyberleader's unit and fired repeatedly until its voice faded into silence. It stood stiffly to attention for a moment and then crashed to the floor in a spectacular shower of sparks.
At once the Doctor turned to the damaged console and began frantically trying to repair the section hit by the blaster.
Nyssa helped Tegan to her feet. 'Doctor, please hurry. We must get Adric off the freighter,' she pleaded.
The Doctor shook his head helplessly and gestured at the shattered instruments.
'Please, Doctor, we must save him...' Tegan cried, turning to the viewer. The Earth almost filled the entire screen.
'I'm sorry. There's too little time,' the Doctor murmured. 'Any moment now the freighter will enter Earth's atmosphere. Nothing can stop it now.'
Adric stood alone on the bridge, staring blankly at the last calculations still remaining to be solved before the third logic code could be broken. However hard he puzzled, the complex mass of figures on the fluorescent screen made no sense whatever to him.
'There's something I've forgotten,' he murmured, absently fingering the torn threads of his tunic where his Mathematical Excellence Badge had been ripped off.
'Something simple but vital I've left out of the matrix...'
Above his head, the main observation monitor was entirely filled with the soft blues, greens and greys of the Earth's swiftly approaching surface. Adric could not help allowing the awesome beauty of the serene planet to distract him for several seconds. When he turned his attention back to the computer display, a sudden obvious error was staring him in the face.
'Of course . . . that's it!' he cried, immediately tapping a fresh set of figures onto the keyboard with feverish haste.
'It's just the reciprocal group of the logarithmic. How could I have been so stupid?'
At that moment, a harsh roar made him spin round. He just had time to glimpse a huge silver shape looming in the entrance and to hurl himself aside before a burst of energy blasted the computer keyboard into a hunk of fused metal. He cowered behind the command seat, sucking his throbbing fingers and staring in frozen terror at the wounded Cyberman swaying drunkenly and trying vainly to aim its blaster at him.
Gradually the Cyberman toppled forward onto its face, exuding a kind of black oily pus from its shattered joints and lay still. Adric scrambled back to the console and gazed for a long time at the utterly useless keyboard. Then he looked up at the huge, luminous image of the Earth rushing towards him and a wry smile spread across his calm round face.
'And now I'll never know if I was right...' he murmured, shivering slightly as if a sudden chill had swept through the bridge, although the instruments were indicating a massive temperature increase in the freighter's structure.
Then he folded his arms very tightly around his body as if to comfort himself and stood waiting quietly for the end which he knew could only be seconds away...
Meanwhile, assisted by Nyssa, the Doctor was desperately fighting to regain control of the TARDIS, which had been thrown out of equilibrium by the Cyberleader's blaster fire. 'We must save Adric...' he gasped, leaning against the jammed levers with all his weight, like an old-fashioned aviator trying to force his biplane out of a crash-dive.
The TARDIS shuddered and groaned, but refused to respond. 'It's no good,'
the Doctor cried, shaking the sweat out of his eyes and glancing at Nyssa in desperation. 'I can't shift her...'
Nyssa added her modest weight to the immovable controls, but they remained completely stuck.
Armed with twisted fragments of Adric's gold-rimmed badge, Tegan had positioned herself behind an interior door to await the return of the Cyber Deputy from his tour of inspection. With thumping heart, she stared up at the viewer which showed the freighter's hull already beginning to glow a dull red from the friction of the Earth's atmosphere as the doomed craft plummeted towards the surface.
'Please, Doctor . . . please hurry . . .' she whispered to herself over and over again, still hoping against hope that the Doctor might succeed in making a last-minute attempt to rescue Adric.
Suddenly the door flew open and the Cyber Deputy strode back into the chamber. At once Tegan ducked out of the way of his powerful arms and started scraping the gold edge of Adric's badge as hard as she could against the grille of his ventilator unit. With one enormous hand the huge automaton clawed frantically at its chest, while with the other it struggled to operate the trigger mechanism of its blaster.
Evil yellow and black bubbles poured out of the ventilator as the stricken Deputy fought against the deadly dust, rattling and gasping in desperation. Tegan dodged about, forcing the flaking gold slivers into the grille with all the strength she could muster.
Seizing the blaster captured from the Cyberleader earlier, the Doctor yelled a warning to Tegan. As she rolled to safety under the console, he fired a long and devastating salvo which quickly reduced the Cyber Deputy to a buckled wreck. The sparking automaton crashed to the floor beneath a pall of greasy smoke and lay motionless.
Tegan scrambled breathlessly to her feet and gazed up at the viewer. She tried to say something, but she could only point silently at the terrible image on the screen.
The freighter was glowing an intense blue-white which was almost unbearable to look at.
Throwing down the blaster, the Doctor hurried over and put his arms round Tegan and Nyssa. Together they watched helplessly the final moments of the incandescent missile, their faces as pale and immobile as plaster masks.
Suddenly a brilliant flash seared their eyeballs as the freighter exploded into a molten cascade of tiny fragments. Then the screen went completely black, as if the stars had abruptly been extinguished. A few seconds later, the TARDIS was shaken by a series of sharp jolts as the shock wave reached it. From the console came a number of quiet clicks as the jammed controls freed themselves.
No one spoke as the Doctor and his two companions watched the glorious patterns of the heavens gradually reappear on the viewer, shimmering silently in the infinite emptiness.
After a while, the Doctor went over to the wreckage of the Cyber Deputy and dislodged what was left of the metal star from the ventilator grille. He stared at it in the palm of his hand for a moment. All the gold edging had vanished.
With a sad smile he dropped it into his pocket and turned resignedly towards the console...