As a result of a lightning strike, commander of the City Watch Sir Samuel Vimes is transported thirty years back, to old Ankh-Morpork on the brink of civil war. The Watch is full of corrupt losers, and among them is only the young Sam Vimes just beginning his service. If he falls under the harmful influence of one of his older comrades, Ankh-Morpork will never get His Grace the Duke of Ankh, Commander of the City Watch, Sir Samuel Vimes. To prevent that, the monks of the History Guild ask Vimes—for the time being—to become John Keel and show himself what it means to be a good policeman by personal example.