I cannot recall a book title that was less well-shaped to its subject. Far from being a “skeptic,” Arthur Koestler was a man not merely convinced but actively enthused by practically any intellectual or political or mental scheme that came his way. When he was in the throes of an allegiance, he positively abhorred doubt, which he sometimes called “bellyaching.” If he was ever dubious about anything, one could say in his defense, it was at least about himself. He was periodically paralyzed by self-reproach and insecurity, and once wrote a defensive third-person preface to one of his later novels (The Age of Longing) in which he described its style as modeled on that of a certain “A. Koestler,” whose writing, “lacking in ornament and distinction, is easy to imitate.” The author himself was written off as “a much afflicted scribe of his time, greedy for pleasure, haunted by guilt, who enjoyed a short vogue and was then forgotten, like the rest of them.”