In the midst of chasing Ankh-Morpork's most punchable psychopath across the rooftops of Unseen University, a freak lightning strike plays havoc with the magical temporal energy around, sending both Sam Vimes and his quarry thirty years into the past. This was a time when the Patrician wasn't quite so sane, the Watch not nearly so upstanding, the City was ready for a Revolution, and a young Sam Vimes had just joined the force but was desperately in need of a decent mentor. (Discworld #29, City Watch #6.) By Terry Pratchett.