Cdan, a historian of the far future, is granted leave to travel back in time to test his theories of intellectual evolution. Establishing a holographic presence to conduct his classes, he is transported to Spelstar, an off-earth entertainment center, where vast data banks and sophisticated computer technology make possible reconstruction of the past from the ancestral trace existing in the brain of each individual. With increasing wonder he relives brief episodes as a succession of his forebearers - a technician in an early lunar colony, a courtier of King Henry III's time, a Viking raider, a medieval novice monk, a Roman senator, and others back to 10,000 B.C. By then, he believes, the true nature of man has become apparent.