Written by H. Beam Piper; it is part of his Paratime series of stories, the first novel published in 1965 was expanded by John F. Carr from 2000 to 2016 to form the Kalvan series
It recounts the adventures of a Pennsylvania state trooper who is accidentally transported to a more backward parallel universe. It was published posthumously, making it Piper’s final science fiction novel.
The Paratime Police patrol the vast number of alternate time-dimensions. Their aim is to keep the existence of the alternate Earths a secret and prevent these Earths from mixing and destroying each other.
But the Time Police make mistakes sometimes, and they make a big one when a seemingly ordinary Pennsylvania State Trooper named Calvin Morrison is accidentally transported to a more backward parallel universe. Morrison is soon being hailed as Lord Kalvan and is masterminding a campaign that could blow the whole Paratime secret sky-high!
