Finally, I was struck by a brainwave. I tracked down one of the younger lecturers in the School, named Tony Howarth. Tony had a rather studious, even anxious disposition, forever glancing around through thick-rimmed glasses. He generally spoke and moved quickly, as if bursting with nervous energy.

The reason I had picked Tony as my confidante was that I had recently discovered that he was a subscriber to the Sceptical Enquirer periodical, as well as being part of an enthusiastic - if slightly nerdy - group dedicated to investigating, and debunking, claims of UFO sightings and ghostly hauntings. He displayed a sharp and enquiring mind, always ready with a plausible mundane explanation for apparently paranormal events.

Sitting in his small office, Tony listened with great interest to my story and then asked a few questions, such as whether I had searched for hidden projectors or wires. I admitted that I had not - it simply had not occurred to me that the presence on the stairs was anything other than completely genuine.

I think Tony could hear the earnestness in my voice and was apparently satisfied that I was not attempting to wind him up as a prank. After a few moments thought, Tony said that he had not heard such a claim but was happy - even eager - to investigate. He said he would make some gentle enquiries around the building and from the University authorities, and asked me to come back the following day.

Tony's report was non-committal. He had explored the area himself and had sensed nothing himself - a situation I had somehow anticipated. He also said that, as far as anyone knew, no-one had ever died in the Computer Science building, but it was impossible to be sure about the residents of the former houses on the site. Finally, Tony said he would talk to some of his contacts through the Enquirer, undertake some further investigations and let me know anything he discovered.

This was a far less positive outcome than I had hoped for, with limited scope for some kind of a resolution. I started to avoid that part of the building, which was always dimly-lit and quiet - especially after dark, when the massed hordes of undergraduates had returned to their usual evening haunts of residential halls and public houses.

Even so, in a hurry one early evening, I casually decided to take that route back to the office. I was shocked and horrified to find Tony, on the floor, apparently dead. The poor man surrounded by a litter of apparatus - assorted cameras, tape recorders, lights and other devices with more obscure purposes - all tied together with a rats' nest of cabling fixed to a latticework of aluminium poles and garden canes with heavy-duty gaffer tape.

I hurried over, desperately trying to remember the rudimentary first aid training I had received several years ago. Tony was definitely dead, already cold and I guessed he had been lying there for an hour or more.

I called out wildly for assistance and, almost immediately George himself appeared around the corner. The old porter leant over, apparently checking the body, then looked up at me shaking his head. Even through my rising panic, I could see he looked somehow satisfied, as if pleased with an outcome long anticipated.

I rushed back down the corridor towards the administrative offices to raise the alarm before collapsing in near-hysterics. I suppose I must have been in shock for a while. I vaguely recall being fed mug after mug of hot sweet tea - something I would normally have avoided - by the secretarial staff.

I imagine that some ambulance crew come to remove the body and senior members of the university management were dragged away from their meetings to handle the situation.

The police cordoned off the entire stairwell using that black and yellow tape familiar to viewers of TV crime dramas, making inconvenient detours necessary. After I had recovered some of my wits, I made a statement to the police, carefully omitting or playing down any the ghostly aspects, and merely noting that I understood Tony to be investigating reports of a haunting at this very spot.

The subsequent police enquiry confirmed the obvious conclusions. It appeared that Tony had been attempting to attach his apparatus to the banisters at the top of the stairs. Somehow, he had fallen and broken his neck colliding with the protruding concrete of the intermediate level, before crashing to the floor below. There was no suggestion of 'foul play', to use that old-fashioned phrase; no evidence that anyone else had been involved.

As a mark of respect, I was present at poor Tony's funeral, which was attended by his weeping patents as well as an eclectic cross-section of the staff and student body. Later that day, there was a short non-denominational service (Tony was an atheist, apparently) in the Department itself, which was rather better attended.

After the funeral and the service, I remained in the Computer building, unsure of what to do. I wandered to the fateful stairwell to find that the police investigation had evidently finished and the barrier tapes had been removed. Absently, I tidied away Tony's equipment, carefully collecting up the damaged instruments and broken cameras. At first, I was not quite sure what to do with it, but eventually I stacked it all neatly in Tony's office, which already seemed unnaturally quiet and faintly dusty, even though the previous occupant had been dead only a few days.

Just as I finished this task, old George appeared at the doorway, the same unaccustomed look of glee in his eyes as I had seen when he had leant over Tony's cooling body.

"What's going on?" I asked, the note of alarm in my voice sounding shrill even to myself.

He made no reply, just stood there looking at me insouciantly. Then he disappeared - by which I do not mean he simply walked away, but quite literally vanished into thin air before my very eyes.

The ghost of Computer Science is more visible, more often, these days. Other people seem to have caught a glimpse of it too, judging from the looks I see on faces emerging from that stairwell. I have not been able to persuade anyone to admit to this, yet, although I do get strange reactions from those of my acquaintances who I questioned just after I had first seen the apparition.

Personally, I am convinced that the ghost in the stairwell is Tony himself. What I had glimpsed before must have been some kind of a future echo, his shade now stronger, more persistent, now that his death is in the past. It seems inappropriately ironic that he was investigating his own ghost when he died - was this the reason for George's nonchalant reaction?

What really worries me now is the old porters astonishing disappearance. The last time I ever saw him was when I was moving poor Tony's equipment back to his office. I spent long hours, night after night, wandering the deserted corridors where previously I would also have guaranteed a meeting, without encountering any sign of him.

The mysterious porter seemed to know more than he was letting on, and I desperately wanted to learn more. I made enquiries, eventually gaining an interview with the Head Porter in the tiny cupboard that his seniority allowed him to use as an office. He was a squat toad of a man, who sat in a decrepit old armchair sipping delicately from a chipped mug of strong steaming tea.

The Head Man told me bluntly that he and the other porters in the building had never heard of George, that they did not recognise the description I put to them. Despite my increasingly frantic protestations, he insisted that no-one of that name had ever been employed as a porter in the School.

So who, or what, is Old George? More importantly, why did he want our local paranormal investigator out of the way? What secret was he desperate to conceal - so desperate that he was willing to arrange Tony's death while investigating his own ghost?

My best guess is that George is a very capable and frankly rather malicious spirit who has been in this location for a long time - much longer than the present building. He did not want to be disturbed and felt threatened by Tony as a potential open-minded ghost-hunter. So the other ghost is both distraction and protection - although I am beginning to wonder about what might be happening on the Other Side...

Part 1 Afterword