What is the main theme of "The Open Window" by Saki?

One important theme of this
satirical short story is revealed in the
symbolism of the characters' names. There is Framton
Nuttel, Mrs. Sappleton and the niece, who is both a "very self-possessed young lady of
fifteen" and a "child." Let's look at these and find the theme alluded
to.

The name Framton indicates
someone who is reclusive and aloof and given to worry and mental tension. This sounds
exactly like the character Saki presents. The surname
Nuttel (Nuttall) is a place name indicating someone who lives in and
tends a nut grove. "Nut" is also slang for a foolish person or a person who is thought
mentally unstable.

Sappleton
appears to be a made-up surname derived from the Old English 'sæp' that has come to be
slang for someone who is foolish and gullible. This perfectly describes Mrs Sappleton in
regards to her manipulative niece.

We learn the niece's
name is Vera, ironically meaning "faith" and "truth." She is the pivotal character, and
we can deduce something about her from her descriptive tags. She has the appearance of
being a mature and trustworthy young lady as she is "very
self-possessed" yet the narrator calls her a
"child" when she begins her
tale:

"Her
great tragedy happened just three years ago," said the child; "that would be since your
sister's time."

The
dominant theme that emerges from the satirically symbolic
character names and this satirical description is that of what foolish, gullible and
mentally strained people do to themselves and allow to be done to others. The mentally
stressed "nut" allows himself to be manipulated and tormented, even by his sister who
insisted he visit this part of the country. The foolish and gullible "sap" allows
herself to be fooled and tricked by her niece and becomes an accomplice to the harm her
remorseless mischief causes to innocent people (one must suppose this is a past-time of
long standing with the self-possessed niece). Thus the
theme is the harm done by foolish and unstable persons to
themselves and to others.

In addition, the niece introduces
the equally strong theme of appearances versus reality. Her
name indicates this theme since she is not very faithful to the truth in what she tells
Framton or her aunt. While she appears to be a self-possessed young lady, she is in
reality a mischievous child, just as while the approaching figures appear to Nuttel to
be ghosts, they are in reality the returning husband and
brothers.

In
the deepening twilight three figures were walking across the lawn towards the window,
they all carried guns under their arms, and one of them was additionally burdened with a
white coat hung over his shoulders. A tired brown spaniel kept close at their
heels.