Harness' first story, "Time Trap", is unusual for a first story in that it shows many of his recurring themes, among them art, time travel, and a hero undergoing a quasi-transcendental experience. His first novel was his most famous, Flight into Yesterday. It was first published as a novella in the May 1949 issue of Startling Stories, was expanded as a full-length novel, and was renamed Paradox Men by Donald Wollheim for reprint as the first half of Ace Double #D-118 in 1955. Much later Harness thanked Wollheim for the title that "turned out to be irresistible". The "science-fiction classic" is both "a tale dominated by space-opera extravagances" and "a severely articulate narrative analysis of the implications of Arnold J. Toynbee's A Study of History." Boucher and McComas described it as "fine swashbuckling adventure... so infinitely intricate that you may never quite understand what it's about." P. Schuyler Miller described it as "action-entertainment, fast-paced enough that you don't stop to bother with inconsistencies or improbabilities." In his introduction in the 1967 Four Squarepaperback reprint of the novel, Brian Aldiss terms it a major example of the "Widescreen Baroque" style in science fiction, and John Clute terms it "the kind of tale which transforms traditional space opera into an arena where a vast array of characters can act their hearts out, where anything can be said with a wink or dead seriously, and any kind of story be told." In Trillion Year Spree, Aldiss and Wingrove report the novel "plays high, wide, and handsome with space and time, buzzes around the solar system like a demented hornet, is witty, profound, and trivial all in one breath." The Paradox Men features the concept of force fields which protect people against high-velocity weapons like guns but not against knives or swords, an idea later used in Frank Herbert's Dune. In 1953, Harness also published his most famous single story, "The Rose", which first appeared in the British magazine Authentic Science Fiction, then as the main novella in a UK mass-market paperback collection. The story did not appear in the United States until 1969. Among Harness' best known stories are "The Rose", "An Ornament to his Profession", "The Alchemist" and "Stalemate in Time". His story "The New Reality" has been called "SF's best Adam & Eve story" by Brian Stableford. His novel Redworld is one of the very few science fiction novels in which all characters are aliens. Harness's ideas influenced numerous writers and he continued to publish until 2001, being nominated for multiple Hugo and Nebula awards. In 2004 he was named Author Emeritus by the Science Fiction and Fantasy Writers of America.
