"The Open Window" by Saki is his probably his most popular story. The dark humor in the twist ending is of the nature few will not enjoy.
The exposition of this story exists with the background of the main character Framton Nuttel. Framton Nuttel is at the house because he has some medical issues, believed to be a hypochondriac, and his doctor has advised rest and the avoidance of excitement or stressful situations. His sister has lived in this area and has given him letters of introduction so he can meet some new people and not be all alone. It is with this back story that Saki makes the ending so evil and humorous.