A magical accident sends Vimes thirty years into the past, to the eve of a revolution he fought in as a young man. Stranded in a younger, meaner Ankh-Morpork, Vimes must guide his own younger self through the coming days - knowing how the revolution ends, knowing who dies, and knowing he can't change it. The finest Discworld novel and one of the great time-travel stories, a book about the difference between a good man and a good copper.