what is the theme of the open window by saki

There are at least three themes aparent in The Open Window, although you might be looking for something particular. The theme appearances and reality might also be considered a theme of deception; whereas the novel also looks at the theme of insanity vs sanity.

If this isn't detailed enough, you might also want to check out a link to one of my prior answers to this question here on gradesaver. The direct link is provided below;

Deception for the sake of practical joke.