My story, yes: it starts one morning, in our 15 minutes. Usually, we steered away from talking schoolwork, but that day I'd brought a transcript in I wanted her to see. Upon the mainframe (this was 1978, they had them then), I'd found a new computer game, Adventure. Standard VR stuff we'd call it now, except that this was single-user, ASCII text, not jack-in neural overrides. Text! Can you quite believe that? Still, we hadn't seen its ilk before, and Maddie was impressed - so much, in fact, she said she'd like to try it out herself.
        And that's how come we both skipped lunch one day, so I could show her. As the teletype (yes, teletype) was noisy, soundproofed space was allocated for it, and that meant we could be us inside, instead of our invented selves. Well, Maddie grasped Adventure's principles immediately: choice points, each a pathway to a different future. Action in the virtual world effected change, resulting in a new world, slightly different from the old. Thus, any world, plus any action, specified a consequential world, so worlds fanned out indefinitely, ever-branching, each an action further from the opening state. Of all these worlds, a few comprised the goal set: playing was a process of discovery, of choosing actions which, applied sequentially, would map a pathway from the starting world through other, different worlds, until a goal world was achieved.
        The next day, we discussed Adventure. Maddie said she wouldn't play it further, as she didn't have the time. I pointed out it had a 'save' command, a meta-action whereby world states could be dumped to disc. She smiled, but still declined, "I'd just fall back on saves if things got tough, select a different path, and try again; it's mechanistic."
        "But," I said, "what if the real world worked like that? What if, ten years from now, you found your life screwed up and had the chance to start again, from here?"
        She laughed, "I guess I'd do it, yes, but surely first I'd have to do a save?"
        "Let's try one then, preserve the instant! Later, we can figure out a way to load it back into reality..!"
        Another laugh, "You're crazy!" but she felt the pull, the niggling insight, maybe it was possible, not then, not ten years thence, but sometime, far-flung in the future; and if not? So, twenty seconds wasted.
        "Right," I said, "we'll need a definition of the moment that we're saving, like a key with which to index into time, to isolate this single point."
        She paused, she nodded, "Well, if time's contiguous, the world we save should be the one immediately following some action. Furthermore, the action should be joint, and something we have never done before nor ever will again." Perhaps. "A kiss?"
        I reeled, the "ever will again" bit got me, and I'm glad it did - the ninety years elapsed since then I would have found unbearable if that had been the price for tracking back. I mumbled, "No, let's slap right hands together, someone might come in, might see us if we kissed."
        Maddie flinched. She almost looked hurt, but she raised her arm, all the same, and then, in unison, we clapped, our left hands held behind our backs.

        Maddie changed. Our 15 minutes fell to 10, and then to 5, before finally they disappeared. I found out later that she alighted one stop early from the bus to buy a snack to have with her lunch. I also noticed that she rôle-played all the time, even when we were alone, and even when I asked her if she'd drop her silly guise and be herself. Maddie, Maddie - why did she want to submerge herself in ordinary, weary, dry existence?
        There was only one occasion, just before we started our exams, when Maddie spoke to me again without charade. I sat, revising, when I heard her voice behind me.
        "What do you think?"
        Turning round, I froze, for Maddie stood there in a skirt, mascara, faintly-tinted lipstick.
        "Why?" I asked.
        She shrugged. "Because I can," she said; she knew my meaning.
        "Will I ever talk to you again?"
        "It's possible, I guess."
        I steeled myself. "Can - can I kiss you, then, goodbye?"
        "Why bother revising maths? It's all just multi-choice isn't it?"
        She'd left me.

        During the Summer vacation, between my first and second years at university, I was back at home. Our town held a small carnival in the first week of July, and it was there that I next saw Maddie, eating an ice cream as she watched the tug-of-war. Her hair was longer, and she was sporting higher heels, but I knew her, knew my Maddie, straight away. Carefully, circuitously, and keeping out of her line of sight, I managed to position myself right next to her before she noticed. For a moment, her eyes flashed in sudden, unconcealed, elated recognition, but almost immediately they reset, doused, took on the dreary-drab indifference of everyday deadness.
        "My husband's in the red team, at the back," she said, surveying her ice cream. "His name is Tom, and he's a doctor." Looking up, she raised her arm, beamed him a smile I knew was meant for me.
        A dark-haired man resplendent in a scarlet rugby shirt waved back. I put his age at maybe 10 years more than ours, which only made him touching 30; at the time, though, I recall, he seemed antique.
        "How do you cope?" I asked.
        "In some ways," she replied, "the lack of hassle compensates."
        "In some ways, yes, but how frustrating!"
        "Well, he loves me."
        "But the waste - "
        "Tom!" she shouted, as the next pull started. "Go for it, Tom!"
        I'd lost her again.

        When was the next time? I may have seen her driving past in a car once when I was home visiting my parents, but it wasn't until the sixth form's 21-year reunion that we actually spoke again.
        I didn't go over to her at once, because my old friends would have seen, wondered why. Instead, I spent an hour or two exchanging general pleasantries and anecdotes, sipping at my Britvic orange juices while about me everyone else got slowly sozzled - well, everyone, that is, except for Maddie. How I thrilled at that - I realised she had not succumbed to hazing out her life, was still alive in there, still vital, still herself, still - somewhere - Maddie.
        The recent nationwide publicity of my appointment as the UK's first Professor of VR had made me something of a celebrity, and I was continually accosted by people from my past who I barely, if at all, remembered. Looking to escape one particularly tenacious woman who was insisting that life was simply marvellous with 6 children, I noticed that Maddie had worked her way around the room and was standing close to the lavatories. Following her plan, I pleaded limited bladder dimensions, and made for the relative sanctuary of the gents. Upon emerging, whom should I bump into but...
        "Hello, Maddie isn't it?"
        She looked absolutely stunning. Older, yes, with one or two small lines upon her face, but how she stood and what she wore showed off a flawless figure. Even I felt grateful that her hair was long now, lush, luxurious, and silk.
        "This noise is giving me a headache," Maddie said, flat, vacantly. "Shall we go out to chat? It's quiet there."
        We did, and Maddie metamorphosed into Maddie once again.
        "There's no-one else," she said. "I thought that what with two of us in our year at school, there must be plenty more, but everywhere I've looked there's none."
        "I know," I answered. "I teach Britain's - Europe's - finest minds, but somehow none of them have quite the flair, imagination, humour, depth..." I sighed. "Perhaps I'm getting far too old..."
        She smiled, her old smile. "Hey, it's me here, Maddie! Why, you great, galumphing - "
        "Excuse me? Madeleine? Is that you? It - it is!" A large-framed, lumbering woman approached from the dark, her face only vaguely recognisable beneath the grout-like cosmetics.
        "Sarah! You made it!" Maddie held out her arms in ostentatious welcome. "Mwwwah!" They kissed 10cm to the right of each other's face.
        "How are you Madeleine? How's Tom? And the children? Oh do let's go inside, who else is here?"
        I wasn't! By then, I'd made it to the safety of my jag.

        That was the last I saw of Maddie until last week. I thought of her often, of what she would be doing, how she might look, whether she still had that spark. Maddie, Maddie, my life's love. How precious those ancient 15 minutes' seemed to me then.
        But at last I had a plan; I'd made my discovery, I'd done it. That's why I emailed her the ticket, that's why I knew she'd come.
        I was honoured guest speaker at the VR conference. The virtual centre in which it was held was crammed with uncountable images, yet Maddie's was distinct, obvious, open. Everyone else was animated, mobile: polymorphic chromaforms swimming in a lake of likeness.
        Maddie was solid, statuesque, with mobile eyes and mouth but little else. The virtual me, alone among the 5,000 VR experts present, appeared similarly. Yes, that's right, I hadn't let the surgeons tap a link into my spinal cord: I still interfaced through my senses, not my nerves. If you let unvetted input charge your brain, then sooner or later something will go in you don't want there. I wouldn't take such risks with my personality, but no-one I explained myself to ever really understood. Maddie, though, the real Maddie, she'd thought out how bad a thing it was, herself.
        Ah, my aged heart - my love still lived!
        After the talk, we met. VR is logged, recorded, monitored, so all we could do then was fix a rendezvous in somewhere real. Next day, my chauffeur drove me to her house, complaining all the way about the distance, then I let him go; I knew I wouldn't need him any more.
        Let me see, now, I haven't had time to think about this, so I'd best describe it just how it happened.
        Maddie was frail, but dignified; noble, even for one approaching the end of her eleventh decade. I'd been in a chair since the early 2060s, but that didn't bother me any now, I was glad still to be there.
        "Maddie," I began, "this is something I've wanted to tell you all my life - all of it. I don't suppose there's much left, now, so I'd best say it today, while I can." I cleared my timeworn throat. "Maddie, I love you. I always have, and I always will, and I wish I'd told you 90 years ago."
        She smiled, that exquisite smile. "We were friends; we respected each other. You thought that if we were lovers, we'd lose all that. We had our minds, but no experience."
        "It was fear of rejection." I coughed. "I couldn't declare my feelings, because knowing you didn't share them would have killed me. This way, at least I had nearly a century of hope."
        Her eyes were wide. "Rejection? By me? You soft - " Tears suddenly began to fall. "I thought, when I offered the kiss, you might accept..."
        "You mean, I rejected you? But - " The truth hit me like a wall. "You hid yourself away, your true self, because you thought your love was unrequited? Oh Maddie!" I put my arm around her, held her tight.
        "Now's a fine time to find out," she sniffed, "we're both nearly dead, I've got great-great-grandchildren." She laughed, sobbed. "But this is simply the happiest moment of my life."
        "Maddie," I said, "listen. I can do it: I can get us back. It's not quite as simple as we dreamed, but it can happen."
        "Map us into a virtual world? What kind of existence is that?"
        "No, I mean here, in reality, in this world. I've tried it, it works."
        "Tried it?" She'd stopped crying.
        "Around five years ago, I figured how to back up to a saved world. All you have to do is to index into the moment. Remember how we slapped our hands, instead of kissing?"
        "If we do that again, we're back?"
        "Yes, but in itself that's not good enough. If we reinstated the world we saved, everything would proceed from then on exactly as before, deterministically. I've looked into this at the sub-quantum level, and it's true even there: any initial state which encapsulates the very means by which it is changed implicitly defines only a single time-line. If we went back to our saved world, then because we were part of the world we saved, we ourselves would be reinstated exactly too. We'd relive precisely similar lives to the ones we have done already, then 90 years later we'd backtrack to the save point again. The same 90 years would cycle through time, again and again, until never!"
        Maddie was nodding, her wrinkled face intense in thought. "So we have to reinstate a slightly different world to the one we saved, where we can somehow remember details from now."
        "Exactly, and it's that which I now know how to do. I'd been taking the wrong approach: I thought that we needed to apply some action to the saved world which would generate a new world identical to it except for our memories. Instead, what we do is save a partial world, just the bits we want to keep, and then try to reinstate that."
        "It sounds to me like it would cause reality to crash..."
        "It does - and that's the crux!" Oh the gladness in witnessing her mind, still so quick, so clear, so dear to me. "The rest of the world is extracted from the previous save!"
        "So it's an incremental dump? And this works?"
        "I can prove it. Think of a nonsense word."
        She did. I thought of one as well, used it as my key to that moment.
        "What's the word?"
        "Balter."
        I thought again, saved the state of my memories, then restored that partial world. It fleshed itself out from the save I'd done just before it.
        "Your word's balter," I said.
        "You asked me?" She smiled. "Of course you did. But that's as far as you can back up now, isn't it? You can't return to an earlier save of your own, because if how you've described it is true, then only the most recent compatibly-saved world can count. To regress any further, you'd need to force a different original dump to be used. That means you now need me!" Her smile became a smirk. "Now suppose I don't co-operate? I'd lose my children, my grand-children, all the friends I've come to know in this reality. Suppose that 90 years of waiting for revenge has twisted me against you? Do you think you could re-run these past twenty seconds enough times to get me eventually to change my mind?"
        For a moment, I felt very, very cold. It hadn't even occurred to me she'd think of that, but she was Maddie, yes, of course, she would, she had done! Oh, the sheer sublimeness of her...
        And how it hurt, so much, to think what awful cruelty unknowingly I'd done that distant instant: 90 years of pain inflicted on her soul. Whatever she now knew I felt, revenge was hers, and justified.
        "It's OK, dear" she grinned, "I'll do it. But you have to promise: I must choose the second key we use, the one discriminating that of this reality which houses our minds."
        The bliss I felt wash over me at that was total, but the second key? "Well, if you like, go right ahead, it's not significant at all."
        "Oh no?" She smiled, "I think it is: a kiss..."