How does the outcome of the conflict between the protagonist and his or her antagonist suggest or illustrate a particular theme?

The protagonist of "The Open Window" is the highly strung Framton Nuttel. He is staying in the country on doctor's orders to help restore his shattered nervous system. His antagonist, the mischievous Vera, expertly spins him a ghost story about a shaggy dog that further damages poor Framton's nerves, causing him to flee in horror. This outcome of the story's central conflict illustrates the theme that appearances can be deceptive.
As part of his rest cure, Framton is visiting a number of families in the local area, and his introductions are provided by his well-meaning sister. The Sappleton residence, where the action takes place, comes across as a large, comfortable upper middle-class house, a perfectly respectable dwelling where the unimaginable horrors experienced by Framton would be most unlikely to occur. Vera skillfully plays upon the unprepossessing appearance of her surroundings to scare Framton with her ghost story. She herself appears to be a fairly normal young lady for her age, which makes her cruel little prank all the more effective.
Both Vera and the sumptuous Edwardian country house lull Framton into a false sense of security, which makes him all the more vulnerable to what happens at the end of the story. The ensuing gap between appearance and reality leads directly to the resolution of the conflict between protagonist and antagonist.