From a recent review in The Weekly Standard of the work of Charles McCarry, a writer of spy novels. McCarry spent several years in the CIA in the 1950s.
The family moved to Geneva, where Charles ("Mac" to his friends) took a job working for the director of the International Labor Office of the United Nations while pursuing operations for the agency. A singleton, "I worked by myself," under deep cover, with great freedom.
McCarry offers little more about his covert work... He does say his description of operations work in his novels is "authentic," but is less vague only when talking about CIA culture. McCarry always describes intelligence work as intelligent work, and the CIA, he found, was full of gifted minds, many with literary tendencies.
"Nothing was so highly valued" at the CIA, he says, "as the ability to write." The writerly mind shares certain functions with espionage work: "An operation," McCarry says, "is a plot."
It makes sense, I suppose, that a spy should write fiction. After all, who know more about plots than a spy?