The borders of the possible

In his dedication for The Thirty-Nine Steps (1915), John Buchan acknowledged that in his thriller the “incidents defy the probabilities, and march just inside the borders of the possible.” (Writing three decades later, Raymond Chandler called this “a pretty good formula” for the genre itself.) All borders were wiped clean with Hitchcock’s 1935 hit film version, which Buchan, ever magnanimous, hailed as better than the original. Graham Greene, by contrast, faulted the director’s “inadequate sense of reality” in adapting the novel. “How inexcusably he spoilt The 39 Steps,” he complained.

Back in 1915, however, Buchan could argue that “the wildest fictions are so much less improbable than the facts” of wartime Europe. By the time a sequel appeared, the following year, he...