It is well known, of course, that being a chef is a very temperamental profession, what with the heat and the excitement and the artistry and so on, and indeed the Fellows of St. Ambrose's would probably have felt cheated if their chef were as calm and collected as an accountant. Poets, painters and chefs owe it to their public to have glamour and tantrums.

But the rapid turnover at St. Ambrose's was quite remarkable. Every few weeks, another advertisement appeared in the local press. One was seen by the aspiring young chef, Gerard Bell, when he was visiting a friend in Oxford. The rates of pay were good; there was plenty of help in the kitchens. Unknowing and innocent, Bell was offered the job on the spot. Accommodation in the college was included, and there was no reason for delay. Bell took up his post immediately, and the Fellows proved most appreciative diners.

The kitchens at St. Ambrose's were very well appointed with all modern appliances, although they had originally been great Tudor vaults, on a grand scale, like all the other foundations of the cardinal who had first endowed the college. The kitchens still preserved the ancient fire-places, with their spits and jacks and roasting-pans, the cruel steel meat-hooks that had held whole sides of beef and venison, the worn chopping-boards a foot thick. Here whole peacocks, roasted, with their feathers put back as trimming, were dished up and carried in to the hall; sucking-pigs with apples in their mouths, goose and swan gilded with saffron, steaming eel pies, almond and cream puddings, all had been lifted in triumph and served at high table, while the students gazed hungrily up from their bread and cheese and ale, sometimes enlivened by a bit of bacon or mutton; the account books listing the pennies and vj pences and groats, and sometimes the guineas that all this had cost, listed year in, year out, were still in existence. Musty and yellowing, they sat in the College Muniment Room.

But modernisation had been the watchword at St. Ambrose's: while the old fire-places and equipment had been carefully preserved and kept bright and polished for the visitors who flocked round, a modern kitchen had been devised within the old, in the vaults of the college. The latest in gas and electric stoves, mixers, microwaves, freezers, and everything the modern chef could desire, had been installed behind the scenes in those parts of the kitchens that were kept private. On the other side of the red ropes that divided the visitors from the life of the college, all was gleaming formica and steel.

So why did the chefs not stay? Young or old, fat or thin, drunk or sober, after a few weeks they invariably packed their bags.

Because of the knives. To the professional chef, the most important items of kitchen equipment are not the whizzers and blenders, not the electric spits or the split-level ovens - none of that gadgetry - but the knives. Good knives, made of the best stainless steel, with sword-like edges, cost a small fortune and have to be kept in immaculate condition. It is the mark of a well-run kitchen that they are always carefully cleaned, sharpened and put back in their proper place after use.

In the hands of an expert cook, the knife will substitute for all the electric choppers and mincers yet invented: it will flash up and down at the speed of light, and the cook will miraculously still have the full complement of fingers at the end of the process. Many chefs will use only their own knives, as archaeologists will have their own trowels and hairdressers their own scissors. They are the tools of the trade, the badge of the professional, as possession of the appropriate lexicons and dictionaries marks out the trade of the scholar.

Bell, a young man just starting out in the world and unable to afford an expensive set, was glad to see that St. Ambrose's was not lacking in knives of the best quality obtainable: in the kitchen, a wooden wall-rack glinted with the bluish silver of the finest steel. There was a complete range, a huge and heavy cleaver for cutting up a whole carcase, saws for the bones, sharp-pointed triangular blades for slitting open, wicked long blades for filleting, down to tiny gleaming slivers that looked like surgical instruments and could perform every intricate operation of dismemberment.

So far, so good. But a week after Mr. Bell had entered on his duties, and the day after he had served a particularly successful Boeuf Wellington followed by peaches flamed in brandy, he entered the kitchen one fine morning and immediately saw that something was wrong with the knife-rack. A long carver was in the wrong place: so, too was the big cleaver. Impatiently, he took them out to re-arrange them, and saw that the edge of the cleaver was dulled and nicked here and there as if it had been brought down with great force.

Naturally, such careless treatment aroused his professional wrath, and he angrily demanded which of the kitchen staff had been meddling with the knives. All denied it. Donald, the sous-chef, was indignant. Maria, who scrubbed vegetables every morning, burst out that she never touched those horrible nasty knives. The kitchen was in a turmoil.

Things settled down, but a few days later there was a similar occurrence. This time it was Donald who found a big carving-knife lying on a table in the older part of the kitchens, its bright blade dulled with brownish stains. Everyone denied having handled it at all, and Bell thought he saw Donald and Maria exchanging an odd look, not a guilty one, but fearful. They seemed reluctant to touch the knife; Bell told Maria to wash it and set it back in the rack and she picked it up gingerly. Like the cleaver, the sharp edge was blunted.

From then on, there were several events: always the knives, always found out of their places and evidently subjected to heavy use. Bell found it inexplicable. He took to locking up the kitchens himself last thing at night, and, before he turned the key in the door, checked that the rack of knives was in order. It made no difference. He took to coming in earlier and earlier, hoping to catch the culprit. Once the air seemed full of the smell of fresh blood, which seemed to choke his throat and nostrils. Once in the grey light of dawn he thought someone rushed past him as he opened the door, and he thought he saw something lying on one of the tables in the old vaulted kitchen: a carcase, somehow familiar. A few seconds later and the illusion vanished.

The business began to prey on his mind. This was the point at which most of his predecessors had packed their bags, but Bell was young and ambitious and determined to get to the bottom of things. At length, he decided that the only course was to keep watch all night, for one of the kitchen staff must somehow be responsible.

So after everyone else had left and the dusk of a winter's evening descended, Bell stayed behind. He had a blanket, and curled up in the massive fireplace of the old hearth, where he was quite hidden in the shadows. Above him, the iron spits dangled in the moonlight. At the other end of the vaults, in the modern part, the rack of knives glinted on the wall.

He had nodded off, it seems, when suddenly he was aware of a shuffling in the stone corridor outside and then the door swung very slowly open. For a few minutes, he could see nothing: there was a dragging sound and then a dark figure, with something wrapped around its head and face, heaved a soft and unresisting burden up onto one of the tables. The figure crossed the kitchens purposefully towards the knife-rack and took down the cleaver: Bell could see it gleaming in the moonlight. Then several big carvers. It went back to the table and laid the knives down, and threw off its hood, yet it had its back to Bell and he could not see the face.

The figure carefully arranged the long object on the table, pulling it into place, stripping some things from it and throwing them towards Bell in the hearth. He shrank back into the shadows, but he had not been noticed - not yet, at any rate. Then the cleaver was raised in the moonlight and brought down with a sickening thud; again and again it fell, yet not in a frenzy, but with the deftness of a butcher jointing a carcase.

Then another knife was brought into play, and Bell recognised it as the skinning blade. A hand, outlined in the moonlight, gripped the skinning knife, slid it sideways into the form lying on the table and peeled off long curling strips which it dropped into a bucket below. It was done neatly, almost systematically, as if with a practised hand.

Bell had watched all this while, as if frozen deep in the shadows of the hearth. But now, after the creature had worked so carefully in the moonlight, the pale light of dawn began to penetrate the kitchens, and it hastened its movements, slashing and chopping frantically as the outline of what lay on the table became clearer to Bell's horrified eye. A ray of sun fell across the table as the busy shape turned anxiously towards the window, and Bell saw its face for a moment. The skin was so pale it seemed almost green in the light, the lips skinny, and the eyes intense and glittering, the eyes of a fanatic. The creature was holding something up, holding it by the hair.

Bell cried out.

Whether it was Bell's voice or the light of dawn that startled it, the creature screamed, tossed down its burden and then scuttled towards the door, pulling its hood over its face. Bell still could not move: as he lay there, the sunlight seemed to dissolve the outlines of the things on and below the table; the last to fade was the shape of a hand.

At last, nothing was left, nothing except the knives and the cleaver, as they had been flung down, smeared with blood and their bright sharp edges notched and blunted.

When Bell went to the Bursar of the college next day, he was expected.

"You lasted longer than most", said the Bursar.

"Who was it?" said Bell.

The Bursar got up from his desk and walked across his office, staring out of the window at the green lawns outside. He turned back towards Bell.

"No sense in pretending I don't know what you're talking about. It's - it was - a student of this college. A poor student. A butcher's apprentice, but a clever boy."

The clever boy had come to the University, but, with no rich friends or relations, was but a half-starved wretch, who could not even afford the cheapest college commons. Pale and emaciated, he sat at the back in the lectures. He crept along to shiver and study in libraries where the ink froze in the winter. He shared a wretched lodging with some half-dozen others like himself. They lived off scraps from the markets. "Like dogs!", he burst out angrily one day. "We live like the dogs in the street!"

We do not know when it first started. His trial probably did not uncover all the crimes he had committed. But when he was dragging his half-starved body through the town, he must have come across someone plump and well-fed, perhaps some pampered girl or a well-off fellow student with the pink skin and arrogant eyes of the rich. Probably in an alley-way, with no prying eyes upon them. What was so special about it, after all? How did it differ from the innocent pigs or calves slaughtered and hung up on hooks in the market? And Providence had placed all to hand. When he had pressed his hungry nose against the windows of the kitchens of St. Ambrose's, drawn by the rich smells of gravy and roasting meat, he had seen the gleaming knives, the chopping boards. Easy to slip into the kitchens at night, do his work while all slept, and then to clean up afterwards and make his way home to the lodging-house.

We know when the companions in his lodging-house first tasted the meat he brought home from the market, for they gave evidence at his trial. He was working for a butcher, he said, who paid him in kind. They accepted this, and, if the meat had a strange taste, and was always chopped into unrecognisably small pieces, they were too hungry to be suspicious, for he was generous and always put a goodly portion in the communal pot as he came into the house in the early morning.

The Bursar turned towards Bell. He took down a hide-bound book from a shelf and leafed through it to a certain page.

"He sold some of it to the college. It was in the accounts" said the Bursar. "Week after week. `Item: to a poor Scholard of this college: for divers flesshe meats at iv pence per lb: ye somme of four shillings and sixpence.'

"He was caught at last. He cleared up carefully, but they saw the knives had been used. It made them suspicious in the kitchens. They dug out the middens and found bones - not from animals. Then some of them hid in the kitchen overnight and caught him at it. I won't tell you what they did to him on the scaffold. Burning him at the stake would have been merciful in comparison. I suppose we can't get you to stay?

No, I was afraid not."