Night Watch by Terry Pratchett

for heavens’ sake, Lu-Tze! This is completely unauthorized, you know! We’re supposed to prune out rogue history loops, not expend vast amounts of time keeping them going!”
    “This one’s important. We owe it to the man. It wasn’t his fault we had the major temporal shattering just as he fell through the dome.”
    “Two timelines running side by side,” moaned Qu. “That’s quite unacceptable, you know. I’m having to use techniques that are completely untried.”
    “Yes, but it’s only a few days.”
    “What about Vimes? Is he strong enough? He’s got no training for this!”
    “He defaults to being a copper. A copper’s a copper, wherever he is.”
    “I really don’t know why I listen to you, Lu-Tze, I really don’t,” said Qu. He glanced at the arena and hurriedly raised his megaphone to his lips. “Don’t hold it that way up! I said don’t hold—”
    There was a thunderclap. Lu-Tze didn’t bother to turn around.
    Qu lifted the megaphone again and said wearily, “All right, someone please go and fetch Brother Kai, will you? Start looking around, oh, two centuries ago. You don’t even use these very useful devices I, er, devise,” he added to Lu-Tze.
    “Don’t need to,” said Lu-Tze. “Got a brain. Anyway, I use the temporal toilet, don’t I?”
    “A privy that discharges ten million years into the past was not a good idea, Sweeper. I’m sorry I let you persuade me.”
    “It’s saving us fourpence a week to Harry King’s bucket boys, Qu, and that’s not to be sneezed at. Is it not written, ‘A penny saved is a penny earned?’ Besides, it all lands in a volcano anyway. Perfectly hygienic.”
    There was another explosion. Qu turned and raised his megaphone.
    “Do not bang the tambourine more than twice!” he bellowed. “It’s tap-tap-throw-duck! Please pay attention!”
    He turned to Sweeper.
    “Four more days at most, Lu-Tze,” he said. “I’m sorry, but after that I can’t hide it in the paperwork. And I’ll be amazed if your man can stand it. It’ll affect his mind sooner or later, however tough you think he is. He’s not in his right time.”
    “We’re learning a lot, though,” Lu-Tze insisted. “For a perfectly logical chain of reasons Vimes ended up back in time even looking rather like Keel! Eyepatch and scar! Is that Narrative Causality, or Historical Imperative, or Just Plain Weird? Are we back to the old theory of the self-correcting history? Is there no such thing as an accident, as the Abbott says? Is every accident just a higher-order design? I’d love to find out!”
    “Four days,” Qu insisted. “Any longer than that and this little exercise will show up, and the Abbot will be very, very annoyed with us.”
    “Right you are, Qu,” said the Sweeper meekly.
    He’ll be annoyed if he has to find out, certainly, he thought as he walked back to the door in the air. He’d been very specific. The Abbott of the History Monks (the Men In Saffron, No Such Monastery…they had many names) couldn’t allow this sort of thing, and he’d taken pains to forbid Lu-Tze from this course of action. He had added, “but when you do, I expect Historical Imperative will win.”

    Sweeper went back to the garden and found Vimes still staring at the empty Baked-Bean Tin of Universal Oneness.
    “Well, Commander?” he said.
    “Are you really like…policemen, for Time?” said Vimes.
    “Well, in a way,” said Sweeper.
    “So…you make sure the good stuff happens?”
    “No, not the good stuff. The right stuff,” said Sweeper. “But frankly, these days, we have our work cut out for us making sure anything happens. We used to think time was like a river, you could row up and down and come back to the same place. Then we found it acted like a sea, so you could go from side to side as well. Then it turned out to be like a ball of water; you could go up and down, too. Currently we think it’s like…oh, lots of spaces, all rolled up. And then there are time jumps,