Of all the unseen characters in literature, one of the most interesting is Mr. Perry, the doctor in Jane Austen’s Emma. Perry, who never actually appears in the novel, is alluded to often, and his wisdom is constantly cited by Emma’s hypochondriacal father. Along with the book’s other background characters, he deepens the world Austen evokes by giving texture to the village of Highbury; he also furthers the plot and allows Austen to get in a little dig at the growing popularity of physicians at the time.

Movies often use unseen characters, and the device is particularly effective since film is a visual medium, where everything else is presented outright. Absence can hang heavily over proceedings, as we see in Hitchcock’s ingenious adaptation of Daphne du Maurier’s novel Rebecc...