“I served under two headmasters,” Miss Pettit said, with the air of a durable politician who has seen prime ministers come and go. “Both deranged. One thought he was God, a not-uncommon delusion in that line of business, I believe. The other went mad in the stationery cupboard at the end of the Christmas term.”

She broke off and leaned forward to see what he had written in his notebook, reading it upside down; a feat, considering her age.

“Personality disorders? Are you going to attribute those words to me?”

“It’s an aide-memoire,” Gareth said. He had been allowed 500 words on Miss Pettit and her library for the centenary issue of the school magazine. Her own centenary fell in the same year. Someone had thought the dual anniversary would make an interesting item.

“I do not care to be paraphrased.”

His 30-minute tape was half-way through its spool; he must have 3,000 words already.

“Of course not, but I may have to - to - ”

“The word you are looking for is precis. There is nothing economical about words like “personality disorders”. Those were simpler times, the man went mad - do stop fiddling with that jotter. All you have to do is take your machine away afterwards and transcribe the tape.

“The first one, God, was quite harmless. He thought that having a chartered librarian on the staff was commensurate with his station in life - Supreme Being. He would bring visitors into the library and introduce me loudly: ‘This is Miss Doreen Pettit, our chartered librarian.’ And to give the man his due, he made full use of my expertise. For 20 years our school library was a beacon. The stock was left entirely to my discretion. I never discarded a book, however old.”

Gareth, making calculations, managed to break in. “That would have been Mr Goodhew, then? He retired in 1964.”

“He was removed in 1964. The chairman of the governors saw himself as a rival deity. We enjoyed an interregnum under the deputy head for six months. It was not enjoyable at the time but in the light of what came after...”

“Mr Barstow?”

“Mr Barstow. The boys called him Mr Bastard, often in public, on the grounds that no one could prove exactly what they had said. He was the embodiment of Shakespeare’s dictum that a man may smile and be a villain.

“Appointed as a moderniser, he detested anything apparently older than himself. Had he been able he would have torn down the very fabric of the building and replaced it with breezeblock. As he could not, he set about destroying the staff. He interrupted lessons, asking impertinent questions; he insulted masters in front of their classes; he carped, he quibbled, smiling all the while.

“He would take an exercise book from a boy who was writing in it and count the pages. If a ring-binder contained blank sheets he would remove them. That was his bete noire, wasted paper. Well, everyone used paper, no one escaped him. Long-serving members of staff began to resign. Then he started on the library.

“The smile would appear around the door, then the inquisition would begin. He paraded me up and down the shelves; why were there so many copies of this? What was the point of that? Did anyone read this kind of stuff nowadays? And always, why was there so much fiction?

“I began to notice that gaps were appearing on the shelves; he was raiding the library by night and removing books.”

“What did he have against fiction?” Gareth murmured. He had recently published a short story.

“It was the ultimate waste of paper. He expected his boys to have more relevant things to read. It was women’s business, we were emasculating the pupils by exposing them to fiction. If they were that way inclined, he implied, let them use the public library.

“I knew his purpose now. He had driven out the music master, the drama specialist and three English teachers, but I was the one he was really after, I - and the printed word. In desperation I invoked a higher authority.”

“The chairman of governors?”

“Some persons of a Christian persuasion have recourse to the scriptures in times of trouble. They take a Bible, and open it at random, trusting that God” - she pointed upwards to differentiate between the god in question and the late Mr Gooodhew - “will direct them to a passage that will solve their problem. I placed my trust in the library angel.”

She’s really lost the plot now, he thought. He scribbled, library angel.

“Don’t squint at me like that. I am not referring to divine guidance. The library angel is a recognised phenomenon, but only by those who have encountered it. You enter a library, in need of information; you have no idea where to begin looking, and yet something directs you to a particular shelf, to take down a particular book, for no good reason as far as you can tell, but it turns out to be the very book you need.

“Sometimes it falls open at the very page you need. Has it never happened to you?”

“Yes, but...”

“That is the library angel. It was a winter’s evening, school was over. Barstow was in the stationery cupboard no doubt, counting his packets of paper. I looked at my depleted shelves. Were I not an atheist I would have cried to very heaven, but as I stood there, cursing in my despair, I found myself drawn to a certain shelf which had survived his depredations and from it, quite involuntarily, drew out a book.

“It was the collected ghost stories of MR James. As I held it, it fell open at Casting the Runes. Perhaps you have read it?

“No, I thought not. It describes how one may ill-wish another by delivering a written malediction into his hands without his knowledge. As you might guess from the title, James’s malediction was inscribed in Runic characters.

“Runes are simply an early Teutonic alphabet, but strange powers are ascribed to them. In the right hands, though, even our Roman ABC can work wonders.

“I replaced the collected stories, returned to my desk and wrote out my malediction in English. Then I stood up, walked to the nearest shelf and took down a book entirely at random, placed the paper in it and left the library. I did not even look at the title of the book.

“The subsequent week was a torture. Every night Barstow bore away my oldest and dearest friends. Once he came to me by day, smiling. ‘These tomes are falling apart in my hands,’ he said. ‘Let’s get something more up-to-date.’

He meant me to know that he was not referring to the books.

“Then, one morning, he did not appear. The secretary telephoned his house - no, he had not returned the previous night. It was, I think, some time after lunch that a demonic ululation was heard to emanate from the stationery cupboard - it was adjacent to his study. When the caretaker unlocked the door he thought at first the ceiling had fallen in. Winters were cold in those days, we had already suffered a substantial snowfall, and that is what the caretaker thought he was seeing - snow, filling the cupboard to waist height and spilling out of the open doorway. In the middle of it Barstow sat, flinging handfuls into the air and uttering inarticulate noises.

“So early in the school year the cupboard had been quite full of paper. He had torn every ream, every quire, every sheet into very small scraps. It was quite amazing how much room it occupied. They had to take him away, of course. I retired the following summer without seeing him again.”

“You cursed him?”

“Hardly,” Miss Pettit said. “That would have been merely crude. Had I wished to do that I could easily have placed the malediction in his hand myself, but then I should have known that I alone would be responsible for whatever followed. No, I had to be sure my cause was just. I left it to the library angel to guide him to the right book.”

“And what was it, the book?” Gareth said.

“As I told you, I did not look at the title,” Miss Pettit said. “Although, as it happened, the cover was the one thing that withstood his frenzy in the stationery cupboard; the complete works of William Shakespeare, in one volume. When I learned that he had been prepared to throw that out I knew he deserved to die. Which he did, soon after.

“Look, your machine has run out of tape. DO switch it off.”

Jan Mark is twice winner of the Carnegie Medal for children’s literature. Her latest novel, “The Eclipse of the Century”, is published by Scholastic Press