The narrator of "Once Upon a Time" first wonders if the sound that wakes her up at night is from her subconscious mind (a sound from a dream) or from her house. She then wonders if the creaking noise she hears is caused by a burglar. However, after listening for a bit, she realizes that the sound comes from the house's foundation creaking in the wind.

All of this frames the story-within-a-story that follows, a story about the futility of trying to keep out what is fearful.

The narrator has in the first paragraph noted that she has been asked to write a children's story. She is planning to say no, she doesn't write children's literature, when the noise waking her in the night and her fear of a home invader stimulates her imagination and leads to the story that follows.

While Gordimer is sleeping at the outset of her short story, she is awakened by noises.  Her mind leaps to the worst possible conclusion at the hearing of these noises.  She begins to think that the sounds might be "an echo- chamber of the subconscious," implying that the sounds heard might be a reflection of her own sense of self.  This could be an insecure identity that projects itself into anything external.  Another conclusion her mind jumps to is that the noises are results of criminal activity:  "...waiting to hear if feet were moving from room to room, coming up the passage- to my door." The reflections of her own fear and the fear of criminal activity from the outside world proves to be the causes she considers until she understands that the sounds or creaking were caused by the old age of her home.