In this story, set on Venus, the sun only comes out for a short time once every seven years. Otherwise, it rains. The story argues for the value of tolerance by showing the effects of intolerance.
Only one child, Margot, among all the nine-year-olds in the classroom where the story is set remembers seeing the sun. Unlike the rest of them, she only came to Venus five years ago. She's different in other ways too: she is pale and frail and seems ghostly. Also, her parents might move back to earth because Venus doesn't agree with her, so her difference looks as if it is getting her privileges. The children are jealous of her and hate her for being different and not conforming to their ways. Just before the sun comes out, they lock in her a dark closet.
The children enjoy the sun. It is a moment of paradise for them. After it ends, they remember Margot and release her, but they feel unhappy about what they have done. One of the messages of the story is that hurting people who are different comes back to haunt the perpetrators too. Their perfect day will forever be a little "clouded" by their uncomfortable memory of what they did to Margot.