Miss Brill is a sad, lonely old woman who doesn't have much in life. The only things she looks forward to are her trips to the regular concerts at the park bandstand. There, she constructs her own little fantasy world, a drama in which she, and the people around her, play their assigned roles. To make this drama vaguely realistic, it's important for Miss Brill to be able to hear what the other "characters" in her "play" are actually saying. Listening in to their conversations provides Miss Brill with additional fuel for her imagination, allowing her little dramas to develop in potentially new and exciting directions.
Sadly, Miss Brill's desire to hear what others are saying results in her public humiliation, and with it, the end of her fantasy drama, which degenerates into outright tragedy.