The students in "All Summer in a Day" live on a fictional version of the planet Venus. It is perpetually raining on Venus, and the storms cease only briefly once every seven years, when, for a few hours, the sun comes out. This transient spell of sunshine is a momentous event for those who live on Venus. The students in the story, aged about nine, are all too young to remember the last time the sun shone, so they look forward to the event with an eagerness that borders on anxiety. When the day finally arrives, they are all gathered in the classroom, watching the rain.
At this point, Bradbury introduces Margot. Margot is not like the other students, who were born on Venus. She is from Earth and only arrived four years ago. She can still remember sunshine as an everyday occurrence. This makes the other children jealous, and they bully Margot in retaliation for the fact that she has seen the sun and they have not.
Margot is as desperate to see the sun shine today as her other classmates, but because she has seen it before—and can remember it—her classmates, led by the spiteful William, decide she doesn't deserve to see the sun this day. They lock her in a cupboard and leave her there when the teacher comes to lead them out into the sunlight. They are pleased to have denied Margot the chance to see the sun, and it is their vengeful satisfaction which makes them smile. The teacher, alas, does not notice that Margot is missing, and it is only after the sun has disappeared once more behind the clouds that the students feel any remorse for what they have done.