"Miss Brill" is about an English spinster living in France, where she supports herself precariously teaching English. We are shown her regular Sunday outing to the park. It is clear from the tone of the description that Miss Brill tends to fantasize her surroundings, as a way of escaping from the dull reality of her solitary life in a "little dark room... like a cupboard" in a foreign country. On this particular Sunday, her fantasties mount higher and higher, until she begins to see the entire spectacle of the Sunday in the park as a gigantic stage play and herself as an important participant:
....Miss Brill discovered what it was that made it so exciting. They were all on the stage. They weren't only the audience, not only looking on, they were acting. Even she had a part and came every Sunday.
However, just as she has established this flattering framing narrative, it is shattered by the careless remarks of a young couple who do not know they are being overheard:
"...Because of that stupid old thing at the end there?" asked the boy. "Why does she come here at all -- who wants her? Why doesn't she keep her silly old mug at home?"
She hurries home, foregoing the rest of her Sunday rituals, and sits on her bed in her dark room, too stunned even to realize that the sound she hears is her own weeping.
The themes of the story seem to be the contingency of happiness and the consequences of careless actions and living in a fantasy world. Miss Brill is happy, but her happiness is based on a fantasy as delicate as a bubble. When the careless couple stupidly allow her to overhear their criticisms of her, she is shattered and driven into a distracted trance. She has been brought face to face with her own insignificance, what she has originally been trying to escape through fantasy, and she cannot handle it.