The Restricted Section of the Library of Unseen University is, primarily, a holding pen for books too dangerous to read.
This is not, of course, a question of censorship. Universities tend to be against that sort of thing, mostly because the professors have enough problems with the students refusing to open their textbooks all year because one glance was enough to tell them that the wretched things were totally unfit for human consumption. Since, in many cases, the professors have written the texts, they have no desire to tell the students that self-censorship is frequently a perfectly rational thing to do.
No, the books in the Restricted Section are not badly written. They are simply bad--cruel, vicious and ancient in the ways of grey, malicious destruction. The Octavo contains the spells that created the Disc, any one of which, if spoken now, could easily take the world apart. The Bumper Fun Grimoire goes in for potentially lethal lunacy. Any one of the rituals in The Joy of Tantric Sex tends to result in the victim looking very happy, very silly and very dead simultaneously. The Necrotelicomnicon--once thought to be the most vile and treacherous of the Books of Power--is capable of driving mortal men insane and making the flesh crawl from their living bones if they merely read a few words.
The thing that few people realise is that books of ancient evil are still being written. People tend to think that just because modern times are modern, ancient evil can't still be around. This is incredibly optimistic, and quite, quite untrue. All a book of ancient evil has to do to be considered ancient is hang about for a few centuries. That's barely the blink of an eyelash as far as the planet is concerned.
And it was one of these modern books of ancient evil that fell into the hands of Unseen University's Librarian.
It didn't look like a book of ancient evil. It looked relentlessly innocent. It was an almost offensively cheerful pink, with three merrily smiling doodles on the cover. And instead of having an author named Achmed the Mad (who preferred to be known as Achmed I Just Get These Headaches), this author called herself Daphne the Awe-Inspiring.
The Librarian stared at the book for a while, unsure what to make of it.
He knew he should go to the alcove near the tomb room where the Necrotelicomnicon was kept and get his mask of iron and smoked glass and his reinforced-with-steel-mesh leather gloves. The problem was, he didn't like leaving a book of which he was ignorant lying about where it could affect all the other magical books. On the other hand, he didn't want to think about what could happen if he brought this book near the Necrotelicomnicon and the two awakened something unspeakable in each other.
Finally, he picked up a ruler and cautiously opened the book with it.
The book was...odd. It appeared to have taken the Morporkian tongue, smashed it with a siege engine and then allowed unimaginative imps to reconstruct the language. It also contained a plethora of rather dull profanity and a pseudo-knowledge of sexuality which would have bewildered any clear-thinking goatherd.
It took rather a long time for the Librarian to figure out what was wrong with the book...well, aside from everything. He was appalled to learn at last that the book was, in itself, an incantation to C'hulagen, Tshup Alkathep and Yob Soddoth--all the ancient and most terrible gods of ignorance and chaos.
There was no way to keep a book that was an incantation to the lords of ignorance in a library. It would suck all the knowledge out of the books, the students and the staff. The Librarian was of the opinion--which, based on his observation of his colleagues, was entirely justified--that human beings did not retain knowledge particularly well as it was.
And he knew he couldn't go back in time and kill the author before the book was written, because he knew NOW that he hadn't killed the author THEN, and if he tried to go back THEN to do so, that would change the NOW to which he was returning, so that in effect he'd be coming back to a parallel dimension while leaving this NOW undefended---
And that way lay madness, even for orangutans.
Nor could he burn the thing. He knew that. He'd stolen books from the Library of Ephebe when it burned a thousand or more years before. He could go back. He knew how to navigate through L-Space well.
But he could not deliberately burn a book. Not even such a book as this.
Yet...he had to protect the Library. He was the Librarian. It was a sacred trust.
He paced back and forth, baring his yellowish teeth now and again at the book.
The answer, when it hit him, surprised him. It was so obvious.
It took him three weeks of normal time and six months of travelling back and forth through L-Space before his arrangements for dealing with the book were completed. In the meantime, the book was kept in a secure room in the catacombs beneath the University, as far from the Necrotelicomnicon and the rest of the Library as possible.
Fortunately, orangutans are appreciably stronger than their discombobulated bodies look. The Librarian only had to carry one box into the catacombs. Two boxes would have meant two trips, and strong as the Librarian was, it's not likely that he would have been fast enough. As it was, he staggered swiftly into the prison-room of the book, and, as quickly as he dared, unpacked the contents of the box.
The Librarian had collected every copy of the book in existence, from Ankh-Morpork to Uberwald, from Fourecks to the Counterweight Continent.
Admittedly, there weren't many copies. The book had been engraved-on-demand, not printed, for the dwarves who ran Ankh-Morpork's presses preferred accuracy. They weren't fond of deliberate misspellings...especially not if the misspelling was a spell.
If he had been human, the Librarian would have blessed them for that. As it was, he didn't give the matter a moment's thought. He simply set the books out in a circle, and opened each one. Then, as the forces of magical ignorance began battering at his mind, he carefully reached into the box, pulled out a manuscript, placed it in the centre of the circle, edged out the door, and firmly locked it behind him.
The Librarian only stayed outside the door for a moment. But that was long enough for him to know that his plan had worked.
A book that devours knowledge will devour the knowledge of the books around it.
If all the copies of that book are put in the same place, they'll devour each other.
"Ook," he said with satisfaction. "Ook."
And he headed cheerfully upstairs to the main Library, grinning as he listened to the munching sounds.