Time and Time Again — H. Beam Piper

John W. Campbell was a man who really knew what makes SF the appealing thing it is; it's no wonder that he published the story. Also included in this volume are "The Mercenaries" (Astounding Science Fiction, March, 1950), "He Walked Around the Horses" (Astounding Science Fiction, April 1948), "The Return" (Astounding Science Fiction, January, 1954 -- a collaboration with John J. McGuire), and "Temple Trouble" (Astounding Science Fiction, April, 1951).