Sam Vimes can't tell what kind of day he's having. One moment he's fighting a ruthless murderer on top of the library of the Unseen University. The next, he's thrown back in time. But, the city's on the brink of revolt, and that killer he was after in the future is with him here in the past, which is now the present. Now all Vimes has to do is figure out how to get back home--but first he has to change the outcome of a bloody rebellion.