Dedicated to Sir Terry Pratchett, OBE, with many thanks, on World Book Day March 5th 2015.

Next to the infinitely large room in which an infinite number of monkeys hammer away at their typewriters, producing such deathless prose as “Shall I compère thee, Thora Summers-Day?”, the Infinity Library stores and catalogues the books the monkeys, and all other writers, produce. It is not, it should be noted, staffed by monkeys, as the task of a librarian is nothing as simple, frivolous and carefree as the task of a writer.

To this library came a girl. She entered via the large main doors, paused for a moment to look around, to the shelves at the left, to the reading tables at the right, then walked up to the main desk and stood there in silence, waiting to be noticed. The current duty librarian glanced at her, held up a remarkably long finger, said “Ook” quietly, and shuffled off. After waiting for a minute, the girl pulled a book out of her bag, and began reading.

After some time, the librarian returned, followed by another. The second librarian - a tall, slender woman with glasses and grey hair - walked up to the girl and sank down on her knees so her face was level with the girl’s. “Hello,” she said. “How can I help you?”

“I’m looking for a book,” the girl said. She put a bookmark in her book, closed it, and put it back in her bag.

“I see. I daresay I can help you with that. However…” The librarian frowned. “Have you tried your local library? We do not usually deal with members of the public here.”

“I look after all the books in our village, and we do not have the book I’m looking for.” The girl hesitated. “We have fiftyseven books, including five Bibles.”

“Oh, I apologise! I did not realise you were a colleague.” The librarian smiled warmly. “Welcome here, dear. Which book are you looking for?”

“Thank you,” the girl bowed. “I’m looking for a book with adventure, which is about a girl like me.”

The librarian studied the girl for a moment. “I see. So it is not a book you have read before, or one you have heard of?”

“No, but there must be a book like it. I think. The adventure books we have are about boys from America, or England or France. That’s fine. But I think girls like me can have adventures too, and I would like to read about those.”

“Oh, you are absolutely correct,” the librarian said. “Come this way, please.”

She led the way to a large cabinet with hundreds of drawers, each a handspan high and half again as wide. “So,” she said, “let us start with fiction.”

She pulled a drawer out, as long as her arm. Along the side of the drawer were more drawers, all the same size as the first. She ran her fingers along those and stopped at one almost by the cabinet. “And then adventure.”

She pulled the second drawer out from the side of the first one. Even though the first drawer was only a hand and half wide, the second drawer kept coming out until it stuck out as far as the girl was tall. Along the side of the second drawer were more drawers again.

“Excuse me.” The girl cleared her throat. “I’m sorry, but how does that work?”

“Well, it is a way of limiting the number of books, by putting more and more restrictions on your search. Here,” the librarian pointed to one of the drawers on the side of the second drawer. “This is female protagonist, so we open that next.” She pulled that drawer open.

“No, I understand that,” the girl said. “I mean, how do the drawers fit together?”

“Ah. Yes, it does seem strange, does it not? I suppose we are all just used to it. To be honest, I do not know. If you are interested, we can see what books there are on the subject later.”

The girl nodded. “I’d like that.”

Together, they kept narrowing down the criteria, both in terms of the protagonist - eight to twelve years old, black hair, brown eyes - and elements of the plot: pirates, treasure, lions, caves, and so on. In the end, the librarian opened a drawer that had no further drawers. Instead, there were some index cards.

The librarian read the cards, glanced at the girl, and put the cards back. “Well,” she said. “The good news is that there is a book like the one you are looking for, but I am afraid it is not currently available.”

“Oh,” the girl said. She thought for a bit. “In that case, maybe we can go back a step or two and find some other book that is a bit like it?”

“Yes, of course.”

There were not many books that fit, even when they widened the search, but in the end they found one that the girl was happy with. The librarian went to retrieve the book, while the girl returned to the main desk, where the duty librarian helped her fill in the form to get a borrower’s card.

“I expect you know this already,” the second librarian said to the girl as she gave her the book, “but the first two rules of this library are ‘Silence’ and 'Books must be returned no later than the last date shown’, both of which are to show respect for other readers.”

The girl nodded. “Yes. Thank you for your help.”

She bowed to the two librarians, put her borrower’s card and the book she had borrowed into her bag, and left the library.

The girl came back a week later, and returned the book. The duty librarian that time was an old man with a huge white beard, skin as black as the night sky, and twinkling eyes. He helped her look for another adventure book about a girl like her. The one she had found first was still unavailable, but there was one set in space that she borrowed.

Over the following years, she read many books and met many librarians, all of whom were helpful and welcoming. The book she had first found remained unavailable, but there were a near infinite number of other books. Even when filtering out those that made no sense (i.e. most, but not all, of the ones written by monkeys), and ones too similar to ones she had read before, there were many good books to read. She no longer insisted that the protagonist must be like her - for that was the single criterion that limited her selection the most - but enjoyed learning to see all the various written worlds through different eyes.

She also read many books about information organisation, archival procedures, and other librarian skills, and eventually found work as a librarian in a large town, some way from the village where she grew up.

One day, when she was young woman in her mid-twenties, she entered the library with a smile, walked up to the main desk and stood there in silence, waiting to be noticed. The current duty librarian, who happened to be the woman who had helped her at her first visit, glanced up, and returned the smile.

“I’m looking for a book,” the young woman said.

The duty librarian gave her a long look, then her eyes widened. “Oh! Yes, of course. Let us see if it is available.”

Together they went to the index cabinet, and found their way to the index card of the book she had asked for the first time. The older librarian nodded. “Yes, it is available. I shall fetch it for you.”

Back at the main desk, the young woman held the book, a huge grin on her face, and bowed to the duty librarian. “Thank you. But I do not need to borrow this, now.”

“It is a good book though,” the librarian said. “I read it after you first asked for it. You should be proud.”

“Oh, I am. And I think I know what the third rule of this library is: 'Do not interfere with the nature of causality’.”

“Very good. But now that you have written it, you can borrow it any time you like.”

“I wonder, though,” the young woman said.

“Yes?”

“There was more than one index card, wasn’t there? Can I borrow any of the other ones?”

“I’m afraid those are not available,” said the librarian. She looked over the rim of her glasses and winked. “Yet.”