Ailsa had been working too hard for too long. Working from home, which you'd think would have been easier, had somehow become the worst thing of all. No distractions, no small-talk chat time away from the screen. Those colleagues she'd thought were irritating and distracting turned out too late, for better or worse it seemed, to have been surprisingly essential for well-being. She was ceasing to feel human anymore. The only relief, and it often seemed scarcely a relief at all, was that after an entire day seated in front of her computer screen with her hands whirring away on the keyboard, at six o' clock she would get out into her car and drive the two miles up to her mother's house to put out her dinner and put on her favourite recorded television shows for her.

Ailsa had read once in a scientific journal that researchers believed there to be five different kinds of human memory. Unfortunately she couldn't remember what they all were now (which is in itself of course quite a funny joke). One of the five had been long-term mechanical stuff like how to drive a car, another one was short-term memory of events only minutes beforehand, another one of things from decades beforehand, such as your childhood. Ailsa's mother had a form of dementia which meant that several or all of these kinds of memory had been being getting progressively eroded over the last few years. On the upside, things that would seem like torture to a normal human being, such as listening over and over again every night to the same 1970s recordings of the Scottish singer Calum Kennedy singing the same sugary-sweet pieces of Scottish song accompanied by tinny accordions, were in fact entirely palatable to her, comforting and pleasurable. Thus demonstrating that complex memory, like so many attributes of advanced intelligence, can sometimes be as much of a curse as a blessing. Without memory, can there be regret? Without the knowledge and imagination to conjure up versions of your possible future, can there be any apprehension and fear? With half your brain missing, you might listen to the same record of Calum Kennedy forever without any ill side-effects. Lucky you.

Ailsa's mother would be most disorientated when waking up after a sleep, such as an afternoon nap. Ailsa would walk in the door, and although her mother would fortunately seem to recognise who she was at some deep level, she would immediately ask Ailsa questions such as: What happened to me? Did I have a stroke? Are my parents still alive? Where am I? Can I afford to live here? This man in the photograph: is he my father or my husband? Where is he? Is he still alive? How old am I? There was often one anomaly in these questions however, that amazed Ailsa, and even began to irritate her over time: no matter how disorientated her mother became, she would nearly always ask after Ailsa's husband, even remembering his name, saying: And how's Raymond?

At first, for the last year, Ailsa had been patiently telling her mother the truth in response to these questions, over and over, meticulously, monotonously. Telling her mother her name, where she was born and grew up, what her parents had been like and what they had done for a living, how many siblings she had, where and how she had met the man she would marry, Ailsa's father. Then one evening, after a particularly stressful day perhaps, or at least a very tiring one, the idea came to her, or maybe it had been creeping up on her from the start, that as an experiment she might try telling her mother something untrue, just to see if she would notice, if she would prove to have any residual intuition that would alert her if Ailsa lied to her. At first, these deviations were very minor. She tried telling her mother she was born in Greenock rather than Paisley, that her father had been a policeman or a greengrocer rather than a postal worker. Her mother did not notice. Lying was something of a new experience to Ailsa and she found; an oddly exhilarating one. Seemingly by coincidence however, the same week that Ailsa began experimenting with these untruths, she returned home one night from seeing her mother to find that her place in her chair at her computer in her study had been taken by an enormous blue-bottle fly. As we have said, Ailsa had been working too long and hard recently, and it would not have been uncommon for her to have sat down there again and continued working from then until bed-time, doing effectively unpaid overtime for her office just to try and catch up with the vast overloaded backlog of work that her team-leader routinely avalanched upon her. But now finally, tonight, she could not. The fly had taken her place and was obstructing her completely, seemingly ignoring her presence, the eerie blue light from the computer screen washing over its vast compound eyes with their metallic grid texture. The thick black hairs protruding from its shiny leathery blue hide twitching slightly as its six long arms all whirred away dexterously at the keyboard in front of it. Ailsa tried clearing her throat, saying Excuse me, is there any chance I could get back in there to get on with my work? But the Blue Bottle just kept on working away, completely ignoring her. Eventually she became enraged, after various other implorements and ultimatums, but was too afraid to touch the monstrous creature, and so had to give up and go and spend the rest of the evening watching television instead.

As it happened, this was the same night that her husband Raymond first failed to come home. At midnight she tried phoning his mobile then his brother to express her concern and try to work out what might have happened to him. After a short embarrassed pause on the phone, Vincent explained to her that Raymond had told him not to disclose to her where he had gone, that he had decided to stay somewhere else for the next few weeks, to get some time away from her, so demoralised had he become with her constant long-hours and consequent bad moods and ill-temper. Nice of him to tell me... she stuttered in shock. And you're assisting him in this are you... this... this.. subterfuge!? What a coward! Can't he even talk to his own wife anymore? When her rage subsided, she found that Vincent had hung up on her. She looked up from where she sat in the living room, and her long view down the hallway culminated in the sight of the Blue Bottle fly still hunched in her chair, attention fixed rigidly on the screen, as its limbs rattled away furiously.

It must have spent all night in the same posture. Unable to decide who to tell or what to do about this unfathomable situation the next morning, she simply made herself a coffee and went into the study and sat down at the sofa a safe distance from the Blue Bottle from where she could just about make out what it was up to on screen. Incredibly, at ten o'clock, her work colleagues hailed her through their usual zoom call and the Blue Bottle fly responded and took its briefing for the day. Standing up and daring to lean in behind its right shoulder, she was able to make out the amazing revelation that her colleagues were not seeing or hearing the Blue Bottle, but her, some semblance of Ailsa, that was still sitting there as before, tapping away at the keys and mechanically answering orders and offering technical advice. Was she going mad? Was she dead, come back in some kind of afterlife? She phoned her brother-in-law again to complain about her errant husband and re-confirm her own corporeality. He certainly wasn't arguing with an imaginary being. So who was this impostor, this Blue Bottle fly that had mastered how to mimic and replace her seemingly down to the slightest detail?

That evening, she made the answers to her mother's usual questions more exotic. She told her mother that her husband had been a commando in World War Two who had been parachuted in behind enemy lines in Germany and made it all the way to Hitler's bunker, where he'd had a conversation with Hitler in German while disguised as his tea boy. That he'd then made it out again and led the Russian army to his location but not before Adolf and Eva Braun has committed suicide. She seemed happy enough with this explanation and very impressed with the bravery her late husband must have displayed throughout this outlandishly daring mission.

That night the Blue Bottle fly finally got tired and came to bed at 2am. Ailsa was horrified at first, but then he climbed delicately on top of her, and she was amazed to discover how light he was. But of course it made sense, that as a flying creature he could not afford to be heavy. Seeing a house fly for the first time at such enlarged scale, in the moonlight filtering in through the voile curtains, she was pleasantly surprised also at how clean he was, how entirely without aroma, contrary to all her previous expectations of how dirty and vile these creatures might be. He was also incredibly gentle and even seemed a little sad, as he rested his big head against her forehead to go to sleep, as if contemplating all the cosmic melancholy of the lost and orphaned creatures of our vast and authorless universe. She felt the dawning of a profound sense of communion with him. She had thoughtlessly killed his comrades about the house for decades, and yet he seemingly understood and forgave her effortlessly. He seemed to simply feel sorry for her for those blind sins, her loss in up to now not appreciating the enormous beauty of his species and their aerial athleticism. He was like an alien, and yet he was strangely familiar, had always been there in the shadows all her life, waiting for this rapprochement. He was like the hidden face of God, it occurred to her as she drifted off to sleep. At least she hoped he was a he. Female flies lay their eggs in corpses, she discovered on the internet the next day, and she was not a corpse she believed, not yet at any rate.

At the breakfast table the next day, he hunched over the table and let drop a discreet pool of white acid on to his jam croissant before leaning down and sucking it up between his masticating mandibles. She found the process much less horrible to watch than people had misrepresented it in horror movies and biological encyclopaedias. In fact it reminded her a little of Raymond ejaculating, the white fluid seeming really no more noxious or repellent than his mysterious excretions from his hairy regions. She stretched her hand out across the table and dared to stroke the long thick black hairs that sprung from his thorax as if he was a pet dog. He brushed his antennae against her cheek and she wondered at what he might feel through those exotic organs.

Knowing herself all too well the grim perils of over-work, she forced the fly to take a short break at lunch by giving him a cup of tea and reading to him from William Blake's Songs Of Innocence And Of Experience:

Little Fly, Thy summer's play, My thoughtless hand has brushed away. Am not I A fly like thee? Or art not thou A man like me?

It was ridiculous of course to wish or imagine that he might talk back to her. But as with a pet dog or a noble horse, she knew deep down that speech might only spoil the bond between them that seemed to reach deeper than all the tedious vagaries of human conversation. He seemed soothed and contented by Blake's poetry about his fellow beings, even if perhaps it was just by the sonorous tone of her voice that she used to deliver it with.

That evening, her answers to her mother's questions became more outlandish again. Ailsa told her how old she was as usual, inviting her to examine her own wrinkled hands as self-evident proof of this, then in a stroke of inspiration told her that rather than approaching death she was being prepared by Mother Nature for a transformation. She told her mother that she was turning into a caterpillar, that would in time after a brief and beautifully transformative sleep, re-emerge into the summer day as a gorgeous and colourful butterfly to flit endlessly about the garden and all the surrounding fields of suburbia. To emphasise the point and get into the spirit of the game, she even went upstairs with her mother and looked out an old sleeping bag for her to crawl into, where she could wait for her wondrous gestation to begin. It seemed a harmless story, a bit of fun to Ailsa that her mother would at any rate have completely forgotten with an hour of her leaving, never mind the next morning.

But returning to her own home afterwards, she was in for a shock. Raymond had returned unexpectedly and was full of shame-faced contrition, begging for her forgiveness for his temporarily abandoning her. Had he not been talking about himself so intensely, he might have heard and be surprised by her first response to him: Where's the fly gone? When he eventually heard her the third time around, his brow furrowed and he joined her in wandering around each room to help her in her search. They were both looking for a house fly, the only difference being in the scale of what they sought, one imagining something small and trapped, the other something strong and strange who had chosen on a whim to stay with her and light up the days of her loneliness with the exotic otherness of his being. When she used the words 'Blue Bottle' to Raymond, he took her to mean her bottle of her favourite gin which he noticed sitting nearly empty in the centre of the kitchen table, evidence perhaps of where she had sought and found solace in his absence these last few days. Before he could reach his hand out to it, she picked it up herself and threw it into the recycling bin with a shiver of revulsion.

When she went up to visit her mother the following evening, she was alarmed to see that the windows to the upstairs bedroom were thrown wide open in the summer evening air and the bed clothes all strewn about her room in confused disarray. The front and back doors were still locked, and yet it seemed that her mother had somehow disappeared entirely from the house. Ailsa felt a wave of panic rising to her throat. Should she phone the police? Ask the neighbours if they had seen her? She had been given to a bit of weeding in the garden of an occasion, but never to actually leaving its boundaries into the terrifying uncertainty of the outside world, a place after all so tumultuous and changeable to her that she had needed Ailsa to describe it afresh to her each day. 

Standing at the edge of her mother's neat green lawn, Ailsa looked down at her mobile phone and began to fumble in the vital digits of the emergency services, until something made her pause. She felt a slight breath of wind from close above, then saw a very large black shadow was spreading across the lawn, as of an object above her, opening its wings.