"Instant of Decision" by Randall Garrett is a science fiction novella published in the early 1950s. The narrative unfolds in a futuristic world grappling with espionage and the geopolitical tensions between the United Nations and the Eurasian League, following a secret agent named Karnes. The story explores themes of reality, surveillance, and the nature of existence, as Karnes discovers that he may not be living in the world he believes to be real. The plot follows Karnes as he undertakes a mission to apprehend a saboteur named Jim Avery, who is suspected of attempting to steal sensitive microfilm linked to advanced technology. After a tense confrontation that results in Avery's death, Karnes comes across an enigmatic object, later identified as a “mind impressor,” which imparts obscure knowledge regarding a larger cosmic scheme. This discovery leads him to question the very nature of his own reality—whether he is part of a genuine existence or merely an actor in a grand historical exhibition orchestrated by a higher intelligence. As the story unfolds, Karnes faces a looming nuclear threat aimed at New York City, ultimately influencing his understanding of history, destiny, and the survival of humanity. (This is an automatically generated summary.)