"All Summer In A Day" is a short story set in a school on Venus some time in the future. It always rains on Venus, and most of the children who live there have never seen the sun. However, the sun does make an appearance for two hours every seven years. The story is set around one of these appearances. One girl, Margot, has seen the sun before, because she is a more recent arrival to Venus than the other children. Margot is a sad, lonely girl, in part because she misses the sun and isn't used to the torrential, constant rain. She, of all the children, is especially looking forward to the sun's appearance, but the other children bully Margot and lock her in a cupboard so that she misses it. At the end of the story, having experienced the sunshine, they better understand why Margot is so sad all the time, and they all feel guilty for what they gave done.
The main themes in this story are perhaps tolerance and empathy. The children who bully Margot don't understand why she is so sad, and, because her sadness isolates her and makes her different from them, they develop a kind of mob mentality and persecute her because of her difference. Indeed, Bradbury writes, "she was different and they knew her difference and kept away."
The other children are also jealous of Margot, who they have heard might be soon returning to Earth, and so they "hate her waiting silence . . . and her possible future."
As Margot is locked in the cupboard the other children run around joyously in the sun, "turning their faces up to the sky and feeling the sun on their cheeks," and "suspended . . . in a blessed sea of no sound and no motion." They are ecstatic, until the rain begins to fall, and then, already missing the sun which they will not see for another seven years, they become sad, and their sadness is like Margot's sadness. Suddenly they understand Margot, and can empathize with her. They go to let her out of the cupboard, wracked with guilt, their "faces ... solemn and pale."
The guilt felt by the other children seems to signal a clear moral, namely that we should not judge or persecute those that we don't understand, but rather make more of an effort to at least tolerate and empathize with them.