Terry Pratchett 
Night Watch [PDF ebook] 

A new stage adaptation of one of Pratchett’s best-selling novels Set in Ankh-Morpork one of the most thoroughly imagined cities in fantasy, Night Watch is the story of Sam Vimes, running hero of the Guards sequence, who finds himself cast back in time to the Ankh-Morpork of his youth. 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."One of the funniest English authors alive" (Independent)