She'd never worn a proper space suit before – never even got close enough to touch one, come to that. They were stiffer than she'd anticipated, and heavier as well. Straker made her strip and put on a blue flight suit first; a surprisingly comfortable garment, warm and smooth against her skin like good quality underwear. She zipped it up and pulled on the pair of fine felted socks he gave her. Then it was time to put on the outer suit.

He was unable to do much to help her get into the suit, but she managed, and he talked her through the process of connecting the air-lines to the Life Support Unit, adjusting the fit and linking to the suit's air supply. He held out each glove in turn while she slid her hands inside and twisted them. They locked with a firm snap and click, and he checked them both before nodding with approval. Then it was his turn.

She watched, unable to do little more than lift the weight of the EMU suit as he struggled into it, hampered by the bandages strapping his fingers together. It took time for him to fasten the seals, and she did not dare help, well aware that her ignorance might cause an fatal error if she did not close the suit correctly. But it was done at last. Then it was time for his gloves.

He'd explained what he was going to do and why, but in the end it was Helen who unfastened the strapping from his fingers and tried to ignore the way he flinched as each bandage was removed. It seemed a brutal thing to do, but even she knew he would be unable to wear the gloves with his fingers as they were. He was working on the premise that the gloves would act as temporary splints and enable him to complete the vital tasks ahead.

Then it was time to put on her helmet. He held it out, let her see how simple it was to wear. "Okay, Helen, you'll have to help me when it comes to fastening my gloves. You know what to do?" She reassured him that, yes, she could do that. He had already explained the controls inside, the radio, the voice activated temperature controls, the drinking tube.

Before he lowered it, he looked at her, eyes staring into hers. "Listen, I don't know how long we'll need to be sealed in these. If there are problems, if it gets unbearable, we can go into one of the emergency compartments and let you take off your helmet, but I'd rather not. Remember, the radio controls are voice activated; and don't panic – I'll be here with you." With that final reassurance he put the helmet over her head and fastened it, locking it into place like a gasket and then the visor slid down, trapping her inside.

For one awful moment she nearly lost control. It was silent and suffocating and utterly terrifying, and she had a momentary sense of what claustrophobia could be like, but she took a deep breath, felt the cool air blowing into the helmet from her air supply, coughed, and heard his voice, calm and soothing as if he was inside the helmet with her. "Helen? Radio test. I need you to count to ten, slowly."

She swallowed. "One, two, three, four – "

"Good. That's working fine. The radio's set so all you have to do is start speaking and I'll hear you. You're doing great. Now, I need you to help with my gloves."

All she had to do was hold the first one out while he pushed his hand into the shape, then she twisted the wrist section and it locked. Then the other. And then they were done.

He touched her arm. A strange sensation, seeing a hand reach out and make contact and yet feeling nothing through the suit. "Good work. Take it slow and don't be afraid to stop me if something feels wrong. Small steps, remember."

"I remember." With the station still under artificial gravity, wearing the suit was akin to wearing full body armour with all its bulk and weight, but she took one step and then the next and so on, until she got into the rhythm. Straker led the way back into the atrium with its control console for the launch bay doors. He had picked up a thin stylus from one of the tool boxes in the launch bay and tucked it into one pocket on the thigh of his suit, and Helen watched as he pulled it out and used the point to type on the console's keyboard, his visor still open and unlocked, in preparation for the last task.

She knew what he was going to do. He had explained it all to her and the thought was terrifying. He was going to use his codes – the passwords that only the verified SHADO commander should be able to use – to access the main computer in the Control Room at the centre of FarSight. Then he would use his authorisation to take control of all the computer systems and change the four-digit code on the emergency compartments – a relatively simple task. But then he would use the same authorisation; the one Fitzpatrick had deliberately not deactivated, to open all the FarSight airlocks automatically, and simultaneously.

All the airlocks. Not just the ones between the domes and at the end of the corridors. All of them. The small emergency access airlocks, the Lunar Shuttle airlock, all of them. Including the huge launch bay doors. They too, would unlock, would slide open. And everything; absolutely everything not fastened down would be sucked out into the Moon's airless landscape. Loose equipment, papers, blankets, mugs, liquids. Humans and aliens. All would be dragged out in the rush of escaping air as the entire atmosphere of FarSight was ripped out through the Launch Bay doors.

Hence the need to be suited up, and after that, once the base had been evacuated, they would head for the control centre. Her radio clicked. His voice, as calm as if he was telling her he'd put the kettle on. "Ready."

She nodded, blushing as she realised he could not see her move her head inside the helmet with its thick visor. "Ready." Her voice sounded strange to her ears, thick and distorted and echoing, trapped in her helmet. She wedged herself behind the console, as instructed, holding on with fingers gripping the edge.

Straker stepped up to the control console, his visor still open. "Command Interface. Voice Print verification. Straker. Edward. Commander–in-Chief. Activate."

"Voice print confirmed. Command Interface activated."

Even Helen knew what that meant – he was still authorised. She could only listen as he worked. "Computer, this is Commander Edward Straker. Code: Lima Echo Oscar Two One Zero Nine. Transfer control of all systems to this station." He waited.

"Transfer complete."

"Straker. Delete all emergency compartment codes. Reset to; zero, zero, zero, zero."

"Codes reset. New code is – zero, zero, zero, zero."

"Straker. Activate command access to emergency airlock protocols through this terminal. Inputting personal command code for emergency control of all airlock systems. Open all airlocks on final command."

"Confirmed. All airlocks to open on completion of command protocols."

Straker closed his visor, and began inputting a set of digits and letters, tapping on the keyboard with the thin stylus. To Helen, kneeling in one corner of the control room, it seemed to take forever. And she was terrified of speaking in case she distracted him and a vital moment. Then he paused, turned to look at her and raised one thumb. A good sign, surely.

She watched him typing, taking his time, making sure of each letter, each digit. At one stage he paused and seemed to falter, but then he shook his head and carried on. One final command and he stepped back. Then he put the stylus in the open pocket on the front of his thigh, next to Alec's diary and the carefully folded blueprint, and moved to stand over her, squashing her in to the corner, pressing her down until she felt that she was going to be crushed by the weight, not only of her suit, but his suit, his body, as well. And then she felt the vibrations through her thick boots, through the heavy fabric of her suit as she leaned against the wall. The clunks and thumps as, throughout the complex, the airtight doors obeyed their new orders.

Wheels spun, doors swung wide, and there was a vast exhalation of air, as if a giant had suddenly puffed out an enormous candle, and the huge launch bay doors slid majestically back, revealing the blackness of space.

It was beyond her worst nightmare. The air filled with a hurricane of papers, liquids, equipment, small consoles torn from their mountings, chairs, a human body, mouth wide open; all rushed past her as she was crushed down there, beneath him. And the aliens, red suited, green-skinned, silent as they were dragged out, as their blood boiled, and their bodies ruptured in the vacuum of space.

She clutched onto the console, knowing that, if she had not been protected by the space suit, if she had been left gasping for the last remnants of oxygen, she too, would have been unable to hang on. It was a horrific way to die. But she could not – would not – regret the manner of their death. They deserved it. She clung on, his weight still on her, his visor touching hers, and she could see that he was watching, not the exodus of his sworn enemies, but her face, concern in his eyes. She looked up at him, as the tornado began to ease and the sounds subsided.

There was one moment of sheer horror, as a red suited figure without a helmet, cartwheeled into the room, one suited arm snagging on the edge of the console. Its eyes, blackened, bulging and blood-filled, seemed to stare sightlessly into her face and the open mouth screamed silent obscenities for a nightmare eternity before Straker managed to unhook the offending arm and push the body away. A final flash of red as it was pulled into the launch bay and out onto the lunar surface by the desperate last gasps of escaping air. Then, all was still, all was silent, apart from the klaxon shrieks of the decompression alarms.

He leaned over her again, not to press her down into the corner, but to help her stand. The heavy suit made it difficult and she was flushed and hot by the time she finally stood upright and she activated the voice operated controls in her suit, grateful that he did not ask her how she was feeling, for she might very well have started crying with either the sheer relief or the sheer awfulness of the whole experience. "What now?"

"We head for Control. From there I should be able to send a message to Moonbase via the satellites. I just hope the aliens haven't already infiltrated Earth's defences."

There was no answer to that. If Earth had been attacked then there was nowhere safe for them now and she cursed Peter Fitzpatrick for his treachery.

It took a long time to get to the dome at the centre of the FarSight complex and, despite all her attempts to regulate her temperature and breathing, she was sweating again and breathless with exertion when they finally entered the space. The artificial gravity was still operating and she felt tired and drained. She wondered how he felt. Exhausted no doubt.

At any other time she might have wanted to explore the complex but not after seeing humans and aliens dragged outside, and anyway, with the entire base decompressed, there was no way that she could remove her helmet though she longed for the touch of cool air on her cheek, and the smell of fresh-cut grass and sunshine and the sound of waves rolling in from the ocean. Earth. Would they see it again or were they both doomed to die here in this bleak outpost, unseen by anyone?

Her radio clicked. "Helen, come and see this." Straker had pulled the blueprint out of the suit pocket on the front of his thigh and spread it out on the chart table, following faint lines on the paper with his gloved fingers and he was calling her over from where she had been staring out of the small viewport at the grey emptiness outside.

She hurried – as much as one could hurry in an EMU suit – to join him. "What have you found?"

He was tracing lines over the paper. "Here. The purification and recycling have been linked directly to this new system. I think this was redesigned to alter the air and water configuration so that the aliens would be able to exist here. If FarSight was going to be a staging post, they'd need an environment as close to their home world habitat as possible. That could be the reason for the insistence on all the airlocks – to contain their atmosphere in the domes and corridors. And the locks on the rooms. I wonder if they planned to use FarSight as a holding pen for people they were going to transport back to their homeworld?" He looked sickened by the thought, knowing that anyone taken from Earth to the alien's world faced a grim and hideous death. "We have to get the SHADO scientists out here to take this place apart. It could give us vital information. But first we have to make sure that Earth is safe."

She watched as he pulled out the thin stylus and started to access the communications system, his hands moving with confidence across the controls as he replayed the last messages from SHADO Command to the FarSight station. "Listen." She heard the urgency in his voice and moved next to him as they listened to the recorded voice of Peter Fitzpatrick's last message as he relayed final instructions to the FarSight station.

"This is Fitzpatrick. Listen up. The initial force is due to arrive eight hours from now which gives you just seven hours to get the codes from Straker. Use the woman if you have to, but you need him alive to activate the command codes. Once he's handed them over, use them to disable all SHADO defence systems ten minutes after the fleet arrives in the Solar System. I will be personally monitoring all transmissions from FarSight from this point on. Do not use the satellite link for any other messages. The home fleet is using the sub-satellite frequency to subvert the SHADO radar systems as they approach. You are to remain in FarSight until after the invasion. Do not acknowledge this message. Fitzpatrick out."

Straker stared at her. "You know what that means – we can't contact Earth and we can't warn them. If I use the satellites, Fitzpatrick will know we have taken FarSight and god only knows what he'd do then. There's nothing else for it but to leave here and try to make for the near side so we can try using the link to SID before Fitzpatrick realises FarSight has fallen. We might be able to contact Moonbase, but even if they do hear us it's unlikely they'd be able to get a rescue craft out to us before our air runs out. I estimate we'd have to travel nearly three hundred miles before we come into range of the Moonbase satellite array that transmits to SID."

"How would we get there?"

"We'd have to use the Moonmobile. The only problem is it has a limited range so we might end up making some of the journey on foot, but it's Earth's only chance. And from the timing of this message we have no more than four hours before the invasion force arrives in the Solar System." And he looked at her in concern, aware that they were unlikely to survive, even if they managed to warn Earth. "I'm sorry, Helen. It's not looking good."

She knew enough to work out the probabilities – that their chance of survival was, to all intents and purposes, non-existent. "Commander?" She needed to reassure him. "It's alright. I understand. Earth is far more important than our lives. Billions of people or us? No contest, so don't feel guilty. I'd do the same in your place." She wanted to hold him, to hug him, to put her hands on either side of his face and to tell him that, yes, it was alright, that she understood, but the space suits made that impossible. So she touched her visor to his and looked at him, her eyes staring into his, accepting that what must be, must be.

And then she smiled at him.

***

Straker finished inputting the last of the commands that would reduce the FarSight computer systems, including the links to the satellite systems, to little more than word processors and adding machines. Helen was already in the ungainly Moonmobile and he hurried to join her, climbing into the small cabin with difficulty. The cabin pressurised and she unfastened her helmet with a sigh of relief, pulling off her gloves and rubbing her numb hands. Straker took off his own helmet and straightened his fingers one by one. He would manage. He would have to. He started the engine and edged the Moonmobile out between the launch bay doors, dust blowing around it as it hovered for moment in the shadow of the FarSight domes.

He looked at the woman in the seat next him. In the light gravity her white hair formed a pale halo around her face. "Ready?"

"Ready." She put one hand on top of his. "Let's go."

Ed Straker turned the mobile in a wide swinging curve, away from FarSight, heading towards Moonbase on the near side of the Moon, in a desperate race to save their planet.