Lord Kalvan of Otherwhen

Lord Kalvan of Otherwhen is a 1965 science fiction novel by H. Beam Piper and is part of his Kalvan series of stories, which is part of his larger Paratime series. It recounts the adventures of a Pennsylvania state trooper who is accidentally transported to a more backward parallel universe. It is Piper's last science fiction novel. The Paratime Police patrolled the vast number of alternate time dimensions. Their aim was to keep the existence of the alternative Earths a secret and prevent these Earths from mixing and destroying each other. But the Time Police made mistakes, and they made a big one when a seemingly ordinary Pennsylvania State Trooper named Calvin Morrison was accidentally switched into the Aryan-Transpacific sector, Styphon's House subsector. In just a few weeks, Morrison was being hailed as Lord Kalvan, and was masterminding a campaign that could blow the whole Paratime secret sky high!