Sam Vimes, The main charictar of this story, was chasing a ruthless villian on the rooftop of the library of the Unseen University when suddenly he falls through the roof and gets thrown back in time. He meets his younger self, and sees a lot of his comrads, but they don’t know him, and they are a lot younger. He gets mistaken for his former commander, the man who taught him how to be a good watchman.
The city’s on the brink of revolt, there’s a curfew, the police are corrupt, and that killer he was after him in the future is with him here in the past, which is now the present…sort of. Now all Vime has to do is figure out how to get back home-but first he has to change the outcome of a horrible revolution. There’s a problem, though: if he wins, he’s got no wife, no child, no future…
Great plot, makes you think, and you can’t tell what the ending is going to be.