First published in 1949, this is the story of John Gordon, a World War II veteran having a hard time adjusting to life in an insurance company. One night, he is telepathically contacted by a man named Zarth Arn, who says that he is calling from 200,000 years in the future. He proposes a temporary mind exchange; Arn will experience life in the primitive distant past, before space travel, and Gor...