Lord Kalvan of Otherwhen
Lord Kalvan of Otherwhen is a 1965 science fiction novel by American writer H. Beam Piper; it is part of his Paratime series of stories, and was expanded by John F. Carr to form the Kalvan series (with some installments co-written by Carr and other writers). It recounts the adventures of a Pennsylvania state trooper who is accidentally transported to a more backward parallel universe.