For most of the last forty-eight hours Donna Yorke had hidden under a desk in a corner of the office where she'd worked since the summer. Without warning her familiar surroundings had become alien, nightmarish and cold. On Tuesday morning she had watched the world around her die. Along with the rest of her work colleagues Donna worked an early shift one week in four. This week it had been her turn to get in first and open the post, switch on the computers and perform various other simple tasks so that the rest of her team could start working as soon as they arrived at their desks. She was glad that everything had happened so early in the day. She'd watched four of her friends die. If it had happened just half an hour later she'd have seen the other sixty-or-so people in the office suffer the same sudden, suffocating death. None of it made any sense. Cold and alone, she was too terrified to even start trying to look for answers. From her ninth floor vantage point she had watched the destruction wash across the world outside like a tidal wave. Being so high above the city she hadn't heard anything. The first sign that something was wrong had been a bright explosion in the near distance, perhaps a quarter of a mile away. She'd watched with morbid fascination as a plume of billowing fire and dense black smoke had spewed up into the grey air from the gutted remains of a burning petrol station.

The cars on the road nearby were scattered and smashed. Something huge had ploughed through the traffic, crossed the dual carriageway and crashed into the pumps, immediately igniting the fuel stores. Had it been an out of control lorry, truck or tanker perhaps? But that had just been the beginning, and the horror and devastation that followed had been relentless and of an unimaginable scale. All across the heavily industrialised east-side of the city she saw people falling to the ground. She could see them writhing and squirming and dying. And more vehicles were stopping too - some crashing and hitting each other, others just slowing to a halt. Donna watched as the destruction moved nearer. Like a shock wave it seemed to travel quickly across the city below her, rolling relentlessly towards her building. With fear making her legs heavy with nerves, she stumbled back and looked round for explanation and reassurance.

One of her colleagues, Joan Alderney, had arrived to start work but by the time Donna had seen her the other woman had dropped to her knees, fighting for breath. Donna was at her side in seconds but there was nothing she could have done. Joan looked up at her with huge, desperate eyes and her body shook with furious, uncontrollable spasms and convulsions as she fought to draw in one last precious breath. Her face quickly drained to an ashen, oxygen-starved blue-grey and her lips were crimson red, stained by blood from the numerous swellings and sores that had ripped open in her throat. As Joan died on the ground next to her Donna was distracted by the sound of Neil Peters, one of the junior managers, collapsing across his desk, showering his paperwork with spittle and blood as he retched and choked and fought for air. Jo Foster - one of her closest friends - was the next to be infected as she walked into the office. Donna watched helplessly as the other girl clawed at her neck and mouthed a hoarse and virtually silent scream of bitter pain, suffocation and fear before falling to the floor. She was dead before she hit the ground.

Finally Trudy Phillips, the last of the early shift, panicked and began to stumble and run towards Donna as the searing, burning pain in her throat began. She had only managed to move a few meters forward before she lost consciousness and fell, dragging a computer off a nearby desk and sending it crashing to the ground, just inches away from where she now lay. Once Trudy was dead the world became still and terrifyingly silent.. Donna's instinctive first reaction was to get out of the office, but as soon as she was outside she regretted having moved. The lifts still worked to take her down to the ground floor (although they had stopped by the time she returned to the building) and their sliding doors opened to reveal a scene of death and destruction on an incomprehensible scale. There were bodies all around the reception area. The security guard who had flirted with her less than half an hour ago was dead at his desk. One of the senior office managers - a man in his late forties called Woodward - lay trapped in the revolving door at the very front of the building, his lifeless face pressed hard against the glass. Jackie Prentice, another one of her work colleagues, was on the floor just a few meters away from her, buried under the weight of two dead men. A thick and quickly congealing dribble of blood had spilled from Jackie's open mouth and gathered in a sticky pool around her blanched face. Without thinking she pushed her way through a side door and stepped out onto the street.

Beyond the walls of the building the devastation had continued for as far as she could see in all directions. She could see hundreds, perhaps thousands of bodies whichever way she looked. Numb and unable to think clearly she walked away from the building and further into town. As she approached the main shopping area of the city the number of bodies had increased to such an extent that, in places, the ground was completely obscured - carpeted with a still warm mass of tangled and twisted human remains. Donna had naturally assumed that she would find others like her who had somehow survived the carnage. It seemed unlikely, even impossible, that she had been the only one to have escaped, but after some two and a half hours of tripping and picking her way through the corpses and shouting for help she had heard nothing and had seen no-one. Occasionally she stopped walking and just stood and stared at the seemingly never-ending disintegration of the world which had appeared so normal and uneventful such a short time earlier. How could this have happened?

What had happened? The sheer magnitude of the ruination was too much for her. Numbed by the massive scale of what had happened she eventually stopped and turned round and stumbled back towards the tall office block. Home was a fifty minute train journey away - more than an hour by car - but Donna had known that going back to her flat would have helped little. Three months into a one year work experience placement from business school, she had chosen to live, study and work in a city over a hundred and fifty miles away from her family home. What she would have given to have been back with her parents in their nondescript little three bedroom semidetached house on the other side of the country. But what would she have found there? Had the effects of whatever had happened here reached as far as her home town? Would her parents have survived like she had or would she have found them dead and... and she knew that she couldn't bear to think about what might or might not have happened to them any longer. The fact of the matter was, she decided, that she was where she was and there was little she could do about it. As impossible, unbelievable and grotesque as her circumstances were, she had no option but to try and pull herself together and find somewhere safe to sit and wait for something - anything - to happen.

The most sensible place was the office she had just left. Its height provided some isolation and it was clean, spacious and relatively comfortable. She knew the layout and she knew where she could find food and drink in the staff restaurant. Best of all, security in the office was tight. Access to the working areas was strictly controlled by electronically tagged passes and from a conversation she'd had with an engineer last week, she knew that the security system itself ran independent of the mains electricity supply. Regardless of what happened to the rest of the building, therefore, power to the locks remained constant, and that meant that she was able to securely shut out the rest of the world until she was ready to face it again. The advantage may only have been a psychological one but it was enough. During the first few long hours of the nightmare that extra layer of security meant everything to her.

Much of the rest of the first day had been spent collecting various supplies, initially from around the office and then, later, from several of the silent shops nearby. She found herself some warmer clothes, a sleeping bag and gas lamps from a camping store, food and drink and a radio and handheld television. By early evening she had carried everything up the many flights of stairs and had made herself a relatively warm and comfortable nest in the furthest corner of the office. As the light quickly faded away into darkness she tried every means available to her to make contact with the outside world. Her mobile phone didn't work. She couldn't even get a dialling tone on any of the office phones (and she tried more than twenty different handsets) and she couldn't find anything other than static and silence on the radio and television.

When the city had become completely dark she gave up trying. The first night took an eternity to pass and the second day even longer. She only emerged from her hiding place on a couple of occasions. Just after dawn she crept around the perimeter of the office and looked down onto the streets below, initially to check whether the situation had changed, but also to confirm that the bizarre and inexplicable events of the previous morning had actually taken place. During the dragging hours just gone Donna had begun to convince herself that the death of many thousands of innocent people couldn't really have happened so swiftly, viciously and without reason. From where she hid underneath the desk Donna caught sight of the foot of Joan Alderney's body, lying where she had fallen and died less than twenty-four hours earlier. Seeing the woman's corpse unnerved her to the point where she was unable to stop staring at it. The closeness of the body was unsettling - whenever she began to think about something else she would see it and it would remind her again of everything that had happened. Eventually she plucked up enough courage to take action.

Fighting to keep her emotions and nausea in check, one at a time she dragged the stiff and contorted bodies of her four work colleagues down to the far end of the office, lay them side by side in the post room and covered them with a dust sheet taken from another floor where decorators had been working. The third morning began in as bleak and hopeless a manner as the second day had ended. A little more confident, Donna crawled out from underneath the desk again and now sat in front of the computer that she usually used, staring at the monochrome reflection of her face in the screen. She had been attempting to distract herself by writing down song lyrics, addresses, the names of the players in the football team she supported and anything else she could remember when she heard the noise. It was coming from the far end of the floor. A tripping, stumbling, crashing sound which immediately made her jump up with unexpected hope and nervous concern. It seemed that her painful isolation was about to end.

Cautiously she crept towards the other end of the long, rectangular building. `Hello,' she hissed, her voice little more than an anxious whisper. `Is anybody there?' No response. She took a few steps further forward and then stopped when she heard another noise. It was coming from the post room. Donna pushed open the heavy swinging door and stood and stared in petrified disbelief. Neil Peters - the man she had watched fall and die in front of her just two days earlier - was moving. Swaying unsteadily on clumsy, uncoordinated feet and stumbling about lethargically, the dead man dragged himself across the room, stopping and turning awkwardly whenever he hit the wall or a desk or other obstruction and was unable to move any further forward. Instinctively Donna reached out and grabbed hold of him. `Neil?' The body stopped moving when she held it. There was no resistance. She looked into its face, its skin greasy-grey and its eyes dark and misted with pupils fully dilated. Its mouth hung open and its chin and neck appeared bruised and were splattered with flecks of dried blood.

With her disgust and abject fear quickly rising she released her grip and, immediately, the dead manager began to move again. It tripped and fell over the bodies of the other three workers on the floor and slowly struggled to pick itself up. Terrified Donna stumbled back out through the doors which swung shut after her, trapping the moving corpse inside. She looked to her right and pulled down on the top of a filing cabinet, sending it crashing down in front of the door and blocking the way out. For a short while longer Donna watched through a small glass window in the door as the shell-like remains of her colleague staggered helplessly around the cluttered room. It moved continually. By chance the body occasionally looked in her direction. Its dry, emotionless eyes seemed to look through her and past her but never directly at her.

Disorientated by the inexplicable reanimation, Donna left the office and began to climb the stairs. The corpse of Sylvia Peters, the office secretary, lay just in front of her on the landing where it had fallen earlier in the week. As she neared the body a slow but very definite movement caught her eye. Donna watched as the fingers on the dead woman's left hand began to slowly move. Sobbing with fear, she turned and ran back to her hiding place on the ninth floor, pausing only to glance out of the nearest window and look down onto the world below.

The same bizarre and illogical thing was happening again and again down at street level. Most bodies remained motionless on the ground but many others were moving. Without reason, explanation or any real degree of control, cadavers which had laid motionless for almost two days were now beginning to move. Picking up her things, Donna made her way to the tenth floor (where she already knew there were no bodies) and locked herself in one of the building's training rooms. There was no sign of the body of the secretary on the landing.