Guards! Guards!

understand.
    “Oh, I see ,” he said eventually. “It’s a sort of humorous play on words, is it?”
    “You know,” said Colon wistfully, peering into the thickening mists rolling in off the Ankh, “s’at times like this I wish old—”
    “You’re not to say it,” said Nobby, swaying a little. “You agreed, we wouldn’t say nothing, it’s no good talking about it.”
    “It was his favorite song,” said Colon sadly. “He was a good light tenor.”
    “Now, Sarge —”
    “He was a righteous man, our Gaskin,” said Colon.
    “We couldn’t of helped it,” said Nobby sulkily.
    “We could have,” said Colon. “We could have run faster.”
    “What happened, then?” said Carrot.
    “He died,” said Nobby, “in the hexecution of his duty.”
    “I told him,” said Colon, taking a swig at the bottle they had brought along to see them through the night, “I told him. Slow down, I said. You’ll do yourself a mischief, I said. I don’t know what got into him, running ahead like that.”
    “I blame the Thieves’ Guild,” said Nobby. “Allowing people like that on the streets—”
    “There was this bloke we saw done a robbery one night,” said Colon miserably. “Right in front of us! And Captain Vimes, he said Come On, and we run, only the point is you shouldn’t run too fast, see. Else you might catch them. Leads to all sorts of problems, catching people—”
    “They don’t like it,” said Nobby. There was a mutter of thunder, and a flurry of rain.
    “They don’t like it,” agreed Colon. “But Gaskin went and forgot, he ran on, went around the corner and, well, this bloke had a couple of mates waiting—”
    “It was his heart really,” said Nobby.
    “Well. Anyway. And there he was,” said Colon. “Captain Vimes was very upset about it. You shouldn’t run fast in the Watch, lad,” he said solemnly. “You can be a fast guard or you can be an old guard, but you can’t be a fast old guard. Poor old Gaskin.”
    “It didn’t ought to be like that,” said Carrot.
    Colon took a pull at the bottle.
    “Well, it is,” he said. Rain bounced on his helmet and trickled down his face.
    “But it didn’t ought to be,” said Carrot flatly.
    “But it is,” said Colon.

    Someone else in the city was also ill at ease. He was the Librarian.
    Sergeant Colon had given him a badge. The Librarian turned it around and around in his big gentle hands, nibbling at it.
    It wasn’t that the city suddenly had a king. Orangs are traditionalists, and you couldn’t get more traditional than a king. But they also liked things neat, and things weren’t neat. Or, rather, they were too neat. Truth and reality were never as neat as this. Sudden heirs to ancient thrones didn’t grow on trees, and he should know.
    Besides, no one was looking for his book. That was human priorities for you.
    The book was the key to it. He was sure of that. Well, there was one way to find out what was in the book. It was a perilous way, but the Librarian ambled along perilous ways all day.
    In the silence of the sleeping library he opened his desk and removed from its deepest recesses a small lantern carefully built to prevent any naked flame being exposed. You couldn’t be too careful with all this paper around…
    He also took a bag of peanuts and, after some thought, a large ball of string. He bit off a short length of the string and used it to tie the badge around his neck, like a talisman. Then he tied one end of the ball to the desk and, after a moment’s contemplation, knuckled off between the bookshelves, paying out the string behind him.
    Knowledge equals power …
    The string was important. After a while the Librarian stopped. He concentrated all his powers of librarianship.
    Power equals energy …
    People were stupid, sometimes. They thought the Library was a dangerous place because of all the magical books, which was true enough, but what made it really one of the most dangerous places there could ever be was the simple fact that it was a library.
    Energy equals matter …
    He swung into an avenue of shelving that was apparently a few feet long and walked along it briskly for half an hour.
    Matter equals mass .
    And mass distorts space. It distorts it into polyfractal L-space.
    So, while the Dewey system has its fine points, when you’re setting out to look something up in the multidimensional folds of L-space what you really need is a ball of string.

    Now the rain was trying hard. It glistened off