'No chatter, this is not a common room.'

     The young man looked up at her, 'I am sorry, but this book, it is too funny.' Rosalind said, 'the book is very funny; something can't be too funny.' But then she noticed the book's title: 'Advanced Quantum Gravitational Modelling.' 'You find that funny?' she asked.

     'Ci, yes,' he replied. 'He has got it all wrong, the writer. I can't believe what he is writing here.'

     'Well,' Rosalind said, 'you should ask your lecturers about that.'

     'They throw me out,' said the student, while staring into her eyes with a deep, latin smile. 'I am Ramon. And you are very pretty.'

     That was how they became an item. Rosalind was attracted to his intellect and found him different and charming. She also liked the fact that not being a native English speaker, he had a reasonable excuse for making grammatical mistakes. Ramon moved in with Rosalind, and they gradually got used to each other's ways. Ramon could be a bit of a slob, but Rosalind forgave him because he could cook. And Rosalind, of course, had her particular hang-up.

     When they'd watch the news together in the evening, Rosalind would point out all the incorrect uses of English, and Ramon would have to persuade her not to stay up all night writing to the BBC. More than once, Rosalind told him how she wished she had a time machine so that she could travel back in time and tell politicians and newsreaders what to say.

     As he didn't have a job, Ramon tended to stay at home during the day while Rosalind went to work at the university. A month or so after moving in, equipment started arriving at the flat, and not long after, it started to hum and beep. Rosalind got used to returning in the evening to find their living area strewn with very complicated-looking scientific apparatus, as well as with papers and books, which seemed to her to contain impenetrable mathematics. Whenever she asked him what it was, he would only say, 'Is secret.' Whatever it was, Ramon was making progress with it. He began to stay up more and more, sometimes working right through the night, muttering to himself, half in his own language, half in technical language.

     Then one day, which happened to be her birthday, Rosalind got back home in the evening to find the flat clean and tidy, with the pleasant aroma of paella in the air and a distinctly self-satisfied-looking Ramon setting the table and offering her a glass of Rioja.

     'Smells good,' she said. 'Where's all the machinery?'

     'Feliz cumpleaños. Happy birthday, Rosalind.'

     'Oh, you remembered!' she said, kissing him. 'I thought you'd be too busy. And this is my present – you tidied up?'

     'Not only this,' he said.

     'You cooked paella too. I love paella.'

     Ramon smiled and said, 'There is more. Close your eyes.'

     'What?'

     'Surprise. Close eyes.' She did.

     'OK, open eyes.'

     She looked. Roman held a tube in his hand, similar in size and shape to a large relay baton. Otherwise, it did not appear, to Rosalind, to be quite of this world. It glowed with an iridescent metallic blue light; each end was surrounded with an aura, through which the light seemed to distort as it passed, as if through an invisible lens.

     'Hold it,' he said, passing her the device.

     'OK. It's very light. I can hardly feel it.'

     Ramon looked particularly pleased with himself. 'Is totally weightless.'

     'Totally? Nothing's totally weightless.'

     'Is when have anti-gravitons balance gravitons in rectilinear time-field containment matrix.'

     'Oh, well, of course.' said Rosalind. 'So what is it? In English.'

     'Is time machine,' he said. Rosalind would have scoffed if her boyfriend hadn't been a scientific genius. Instead, her eyes widened, and she went a little pale. She took a drink of wine and gulped it down.

     Ramon explained, 'You said 'I wish I had a time machine', so I build one.'

     Rosalind continued to examine the device with wonder. 'Lots of people say I wish I had a time machine. They don't get one.'

     'Lots of people aren't my girlfriend. So, where you wanna go? It will take us into the past and return us to the present.'

     'You're not serious? Surely? Not a real time machine?'

     'Serious. It work.'

     'Is it safe?'

     'Safe. But…'

     'But what?,' she asked, quite certain this would be the most vital of 'but's.

     'If we are very carefully,' he replied. 'Only one trip. Use once. Is all.'

     Ramon explained in his most earnest of tones, that there might be disastrous consequences if they changed anything while in the past. And travelling to the same time more than once was absolutely forbidden: you might meet yourself. Therefore, he decided to place a limitation on the time machine. It could only be used for one trip into the past and back again. A very special, one-off birthday present. After that, for safety, the circuitry would self-annihilate. Rosalind didn't have to think for very long. With only one trip possible and the whole of history to choose from, there was never any doubt in her mind. It was a matter of making the world a better place, of righting a wrong that otherwise would be left for eternity to tarnish the crowning achievement of humankind. And, after all, she would only have to persuade Roman to allow her to make the tiniest of changes; a single word; just one letter in fact. One, small change for Mankind.

     *

     'Boring, boring,' whispered Ramon.

     'Shush,' whispered back Rosalind.

     They were on the Kennedy Space Centre tour. 'Can't we go now? Just do it?' asked Ramon impatiently.

     'No. Remember the plan. We're not in the right place yet. Just wait.'

     Ramon tugged on the straps for his backpack, as he had done countless times that morning.

     'Anyway, it's quite interesting,' said Rosalind. 'After all, it was from here that Man first reached for the stars.'

     'Yeah,' said Ramon.

     The tour party, about twenty people, was being led through some bland corridors by a guide, who stopped the group momentarily to inform them, 'The offices in this corridor are used by NASA's army of support and administrative staff.'

     Ramon sighed almost audibly.

     'Shush,' urged Rosalind again, whispering. 'We don't want to draw any attention to ourselves. Just think, maybe the Apollo astronauts used these very offices.'

     Ramon put his hand up and asked, in a loud voice, 'Scuse me, Mr guide, these office used by Apollo astronauts?'

     'Ah no, Sir, they were in a whole other building.'

     'See?' whispered Ramon.

     'Be patient,' Rosalind whispered back.

     'I thought maybe we meet an astronaut,' moaned Ramon.

     'We're going to, remember?' said Rosalind.

     The tour party arrived in a large room with many monitor screens and control panels. While the rest of the group looked around with interest and took pictures, Rosalind and Ramon hung back a little.

     'Right,' said Rosalind, 'I think we're nearly there. Let's go over it again.'

     'Again?' said Ramon.

     'Yes, again. We can't afford any mistakes. The date and time?'

     '16 July 1969. 4.37 AM, local time,' said Ramon automatically.

     Rosalind said, 'Right. And…?'

     'And when we arrive, we have to be quiet like mouses.'

     'As mice. Right.' Rosalind pecked him on the cheek. 'Good. Love you.'

     They took a few selfies in order to look like ordinary members of the group, then the guide ushered everyone along the corridor to the next room.

     'OK, folks. Around the walls in here you're gonna' find displays tellin' ya' all 'bout the different projects: Mercury, Gemini, Apollo, the Shuttle, and all the technical information 'bout the spacecraft. Feel free to wander round and look at the displays. We'll take twenty minutes in here.'

     Rosalind held Ramon's hand and squeezed it tight. This was the place.

     'Just think,' she whispered, 'a few minutes from now, we'll be changing history. Fixing it.'

     Ramon only said, 'I hope careful.'

     The guide went on, 'This room, interestingly enough, used to be the crew locker room in the Apollo days, which the crews used before transferring to the suit-up room where they put on their spacesuits. That suit-up room is right down the corridor, and we'll be heading there next…'

     The group filed in and spread around the room to read the displays. Ramon and Rosalind had done their homework. They knew exactly what this room used to be. They looked casually at the displays around the room.

     As an information resource, Rosalind thought, it was well set up. The boards explained all about each mission, and there were many pictures. The tourists could also listen on headphones to the authentic recordings of iconic exchanges between astronauts and controllers. Ramon and Rosalind found the section on Apollo 11.

     'Look at this,' said Rosalind. She pointed to the display that was all about Neil Armstrong's first steps on the moon. His famous words were printed on the display, and you could listen to them on the headphones too, 'That's one small step for man, one giant leap for mankind.' Rosalind exchanged a knowing look with Ramon.

     They backed away from the rest of the group.

     'Right,' said Rosalind in a low voice, 'when we arrive, this room will be locked. The crew will already have transferred to the suiting up room. There'll be a guard on the door outside. Then – well, you tell me the rest.'

     Ramon said, 'Then, four-forty, a technician come in with the guard, looking for something.'

     'A lucky charm.'

     'Yes. Mrs Aldrin give it to Buzz Aldrin the night before, but he forget it. Is in the bag he leave in his locker.'

     'Good. But, they won't see us because…?'

     'Because we gonna hide behind the door.'

     After a while, the guide said, 'OK, folks. Time to move on. Hope you found this interesting. Now if you'll follow me, we'll head down the corridor to the suiting up room.'

     The tourists started to file out. Rosalind turned to Ramon. 'Is the device set?'

     'You know it is.' Using his body to hide it from the other tourists, he took the glowing tube out of his bag. They lingered at a display until nobody else was left in the room.

     'OK. Rosalind, remember. Stick to the plan. Don't change nothing else.'

     'Of course. One small fix for Man.'

     'Yeah,' agreed Ramon, 'One small fix.' He kissed her, then guided her hand so they were both holding the device. 'Let's go. I press… now.'

     Instantly, the room went dark, the displays disappeared, lockers replaced them, and it smelt different.

     'It worked,' whispered Ramon. 'July 16, 1969.'

     'The right time?' asked Rosalind. 'Four-thirty-seven am. Yes.'

     'OK, clothes,' Rosalind instructed. They both opened their backpacks as quietly as possible, fetched out white coats, overshoes, and hats, and put them on.

     Ramon felt in his bag and brought out two badges. He gave one to Rosalind. 'Fake ID's'.

     Their eyes were starting to adapt to the dark. Rosalind looked around. She motioned to Ramon to look at the names on the lockers: 'Armstrong,' 'Aldrin,' 'Collins.'

     He mouthed, 'Cool.'

     She mouthed, 'Very cool.'

     They stashed their backpacks out of sight, then went and stood tight together behind the door. At four-forty, just as predicted, they heard voices approaching in the corridor. 'Can y' open up? Aldrin forgot somethin'.'

     'Sure thing, sir.'

     Rosalind and Ramon heard the door being unlocked. It opened, and the lights came on. In walked a technician and the guard.

     'He forgot something?'

     'Yeah. A lucky charm.'

     'Like a necklace or somethin'?'

     'Yeah, like that. With a stone on it. Emerald, he said.'

     By the time they had said this, Rosalind and Ramon were hurrying along the corridor to the suiting up room.

     'Slow down.' said Rosalind. 'Calm. Look natural.'

     'Right. We technicians.'

     'Exactly. Nothing special about us.'

     'Except we gonna change history.'

     They approached the suiting-up room. 'OK, here we go. Remember, be cool. Like we work here every day.'

     A man in military uniform stood guard. Two technicians came out, chatting about something technical. Rosalind and Ramon did the same. 'So, did you check the settings?' said Rosalind loudly. 'I did…madam,' replied Ramon.

     'Check your passes, please,' said the guard. They held their breath, but Ramon's forgery skills were obviously good enough because they were waved in.

     It was a longish, white-walled room with bright lighting. The three astronauts were seated in big armchairs, wearing their white space suits but not helmets. There were two or three technicians with each, chatting in a low-key but professionally-assured way. Aldrin was closest to the door, then Collins, then Neil Armstrong at the far end. Rosalind had to pinch herself. This was history in the making.

     Looking as nonchalant as possible, Rosalind and Ramon made their way along the room, heading for Armstrong but after only a few seconds became aware that the chat from the other technicians had stopped. When they reached Armstrong, his technicians looked up.

     'Hey, who are you, fellas?'

     Ramon distracted them for a moment, 'Hey guys,' he said, 'Can you help me over here with this O2 pressure gauge? I think is not working right.' He led two technicians over to a bank of instruments. 'Which gauge? Hey, who are you anyway, buddy?'

     Rosalind seized her chance. She crouched down to the side of Armstrong.

     'Sir, Commander, don't say, That's one small step for man, one giant leap for mankind, because man and mankind are the same thing. Say one small step for A man. Then it's meaningful. Remember Commander, A man, not man.' Armstrong said, 'What…Who..? How?'

     But they were off. Rosalind ran, grabbed Ramon, and together they skipped through the door, past the guard, and sprinted down the corridor. They heard a technician behind asking the guard, 'Those guys show you ID?'

     'Yes, they did, Sir.'

     They came to a corner and slowed to a walk. As they rounded it, they saw the guard still on duty at the locker room door.

     'Let me handle this,' said Rosalind. They strode up to him. 'Brown from err launch admin,' she said. 'Open it, then you're wanted in the suiting room.'

     The guard complained, 'But…,'

     Rosalind said, 'No chatter. This isn't a common room.'

     The confused guard replied, 'Err… No, ma'am. Yes, ma'am.' He opened the door, then walked smartly off.

     Hurrying into the room and recovering their bags, Ramon said, 'You're good.'

     Rosalind said, 'I know. Bossy librarian act.'

     Ramon got out the device, turned it on, they both held it, and Rosalind said, 'Let's get out of here.'

     The same room they had left ten minutes before rematerialised around them, with the last member of the tour group just walking out.

     They looked around, then looked at each other. Both breathed heavily. Then smiled.

     'We did it,' said Rosalind.

     'You did it. I help.'

     The time travel device made a fizzing sound, there was a whiff of burning, and the glowing lights stopped. 'No going back?' asked Rosalind.

     'No going back,' Roman confirmed.

     'Good,' said Rosalind, 'A job well done. History has been changed, and a terrible mistake, overshadowing one of the greatest achievements – no, THE greatest achievement – of mankind, has been erased.' She threw her arms around his neck and gave him a big kiss.

     'Cool,' said Ramon. Then he noticed a photo on the display boards. 'Rosalind. Check it out.'

     They stared together at a grainy picture of two characters in white technician overalls, apparently running along a corridor. Next to the picture was the caption, 'Who were the mysterious technicians?'

     'That's us!' said Rosalind. 'From just a minute ago.'

     'From fifty years ago. Yes, is us. They must photograph us on security camera. I knew it was not safe.'

     'Oh, no harm done, surely. We've probably had everyone speculating about us for decades. What a hoot. The main thing is …'

     But Ramon cut her off. He had noticed something else. 'Rosalind. This part, is different, no?'

     She scanned the display. At first she was pleased to see there was no longer anything about 'One small step for man, one giant leap for mankind.' Then she read out the new caption, 'Listen to the full transmission as, overwhelmed by the weight of history, a tongue-tied commander Armstrong sets foot on the lunar surface.'

     She turned to Ramon. 'No. No, no, no, no, no!'

     'What?' he said.

     Rosalind didn't speak but put on the headphones and listened. Roman watched as the blood drained out of her face like she'd drunk bleach. Hands shaking, she handed the headset to Roman and slumped down onto the floor.

     'Not good?' he asked. 'We fixed it, no? Good grammar now?'

     'We have to go back.'

     'No possible, Rosalind.'

     Rosalind put her head in her hands as Ramon put on the headphones and listened to the recording:

     ARMSTRONG: 'OK, I'm gonna step off the LEM now. That's one small step for man… for A man; one giant leap for man… a man… a mankind… a giant leap for… every people… for, you know… for us… all, for everyone… hell, for all of humanity… I mean… I did it, but it's for everyone, y'see?…'

     MISSION CONTROL: 'Thank you, Neil. Err… beautiful words.'

     BUZZ ALDRIN: 'Say, Neil, you wanna try goin' down that ladder again?'

     Ramon removed the headphones. He tapped the disconsolate Rosalind on her shoulder. 'I could say better, no?'