Occasionally the Librarian would stop, and sniff at the books nearest to him. At last he said 'ook', quietly, and pointed to another stack of books. There were, drawn gently on the spine of an old leather-bound volume, some chalk marks.

'Librarian-sign,' said Rincewind. 'He's been here before. We're close to Roundworld book-space.'

'How could he—' Ponder began, and then said: 'Oh. I see. Er ... Roundworld exists in L-space even before we created it? I mean yes, obviously I know that's true, but even so—'

Rincewind took a book from a pile near him. The cover was brightly coloured and made of paper, suggesting an absence of cows on the originating world, and had the title: Sleep Well My Lovely Falcon. The words inside made even less sense.

'It might not have been worth our trouble,' he said.

The Librarian said 'ook', which Rincewind understood as 'I'm going to get into real trouble with the Secret Masters of the Library for this day's work'.

Then the ape appeared to triangulate on the bookscape around him and knuckled forward, and vanished.

Ponder looked at Rincewind. 'Did you see how he did that?' he said and then a hairy red arm appeared out of the air and jerked him off his feet. A moment later the same thing happened to Rincewind.

It wasn't much of a library, but Rincewind knew how this worked. Two books were a library - for a lot of people, two books were an enormous library. But even one book could be a library, if it was a book that made a big enough dimple in L-space. A book with a title like 100 Ways with Broccoli was unlikely to be one such, whereas A Relationship Between Capital and labour might be, especially if it has an appendix on making explosives. The deeply magical and interminably ancient volumes in the Library of UU strained the fabric L-space like a baby elephant on a worn- out trampoline, leaving it so thin that the Library was a potent and easy portal.

Sometimes, though, even one book could do that. Even one line. Even one word, in the right place and the right time.

The room was large, panelled and sparsely furnished. Quite a lot of paperwork was strewn on a desk. Quill pens lay by an inkwell. A window looked out on to broad gardens, where it was raining. A skull lent a homely touch.