Night Watch

Sam Vimes, running hero of the Guards sequence, finds himself cast back in time to the Ankh-Morpork of his youth--a much nastier city, with an actively deranged Patrician and a sadistic secret police--and finding himself filling in for Keel, the tough honest copper who teaches the young Vimes everything he knows. And, more worryingly, who dies heroically in the insurrection Vimes knows to be imminent. With a psychopath from his own time rising in the vile ranks of the Cable Street Unmentionables complicating things, Vimes has to ensure that history takes its course so that he will have the right future to go back to, and to keep his younger self alive.