Undeterred, we decided to return a few days later, during daylight hours, to install motion-sensitive cameras. This was a spectacular failure, with no movement triggering the cameras, nothing at all from the automation. We tried it out on several nights, testing it by moving nearby ourselves, but without success.

Our attempts at using automation having failed, we made a second visit as a group, again holding a night-long vigil. Much as before, the cameras showed dark shadows against the stonework, and the team members all reported the same churning feeling of dread and some half-sensed movements in the gloom. There was nothing conclusive, no evidence which would have swayed the sceptical observers we had all convinced ourselves that we were, but the feeling that there was something just beyond our observation was indubitable to those present.

We made further attempts, deploying different equipment and using a variety of technology as well as the vigilance of the team members, but to no avail. One by one, the team members began to lose interest: there was nothing to observe, nothing concrete, and even the local paper ceased to be interested. By mid-December, we had disbanded, each of us beginning to follow other interests and projects, including the demands of the University lectures and courses we were supposed to be attending.

In any case, the students amongst us would soon be leaving for home and family during the Christmas break. I had delayed my return to the parental home for a few days, not particularly wanting to leave behind the freedoms of the student lifestyle just yet and returning to the rather more constrained conditions I endured when living with my father and mother. I still had some curiosity about the old bridge, some sense, perhaps of unfinished business, or maybe I wondered if there was still something more enlightening that I could discover.

So, on that weekend just after the end of term, I packed a rucksack and caught a late train to Hebden Bridge. I made my way from the station to the old bridge, skirting the hostelries which seemed so much more inviting that the prospect of a long and lonely evening in the open air. I felt the by now almost familiar sinking feeling in my stomach as I drew near, and it took all my willpower not to turn away. It was so much harder on my own without the moral support, or perhaps just the macho competitiveness, of my comrades to push me forward.

I stepped onto the bridge itself, making my way slowly towards the other side. I could hear nothing other than the rush of the water which seemed to drown out all other sounds - the chatter of drinkers and the clink of glasses in the pubs and bars on the riverside, the rumble of the distant traffic, even the bass-line thud of the jukeboxes and nightclubs. I felt as if I was the only person for miles around, all alone in a world of stone and water.

I edged towards the centre of the bridge, fumbling in my anorak pocket for my digital camera. I thought I caught a movement behind me in the corner of my eye, and I spun around, pressing the camera release almost instinctively. There might have been a movement in the shadows, I could not tell for sure - perhaps some presence, only felt rather than seen. I was convinced that there had, for a split second, been someone there.

At that moment, I abandoned my plans for a long stay and set off at a fast walk - not quite a run - back to the railway station, pocketing the camera as I did so. It was only when I was safely on the train that I thought to inspect the snap I had taken. Using the little screen built into the back of the camera, I pulled up the image I had captured. There, in the picture, stood a dark shadow against the stonework of the parapet, a dark bulky form that could have been any of the old investigation team.

At first I wondered if I had inadvertently looked at an older image, one taken during the numerous previous visits, one showing a picture of a member of the team, and I had not actually taken a new photograph at all. With growing horror, I realised that I was wrong. It was definitely the viewpoint I remembered, and the shadowy figure in the image looked as if it had oozed from the very stones themselves. In a flash of insight, I realised that all of the other images showing team members we have taken before were of the same shadowy form.

As I sat staring at the image on the back of the camera, something came back to me that I had read about when researching tales and legends surrounding the old bridge. The stories told of the making of a living offering to strengthen the stones, the blood to fortify the mortar. I had assumed that the sacrifice would have been a sheep or a goat, but now I was not so sure.

I was of course aware of the old ritual of appeasing the spirits of the river before crossing by throwing a coin, an offering into the surging waters. This is observed even these days, when people instinctively taking a copper from their pocket to thrown into any running water they encounter, to appease the ancient spirits.

The making of a human sacrifice was a pagan ritual which would have been severely frowned upon by the Church, were it to have been discovered, but whose existence could not be entirely discounted. I was convinced that the rough workmen who were engaged to cut the stones and assemble the arches also engaged in a dark and heathen ritual.

I sat on the train, shivering in the meagre warmth and stark lighting. To my horror, I could not stop myself imagining the feelings of the sacrificial victim. I could see it all so clearly in my mind's eye. I felt sure that he was chosen to be a big strong lad to make sure, I suppose, the bridge was equally strong - old-school sympathetic magic, I now realise.

Even now, I can picture the poor young man, all alone, restrained, chained, in the dark and the rain, knowing that he was going to be cut open and his blood poured over the stones and mixed into the mortar, and only able to contemplate his own shadow in the mist and firelight.

Now the stones endure, and his blood and his spirit endure also.

Part 1 Afterword