What if everything we thought we knew about the universe were proven wrong all at once? Kalgash is a planet that is perpetually bathed in sunlight.

Its people have lived for a multitude of generations thinking that everything they could see was all there was to the universe. They could see their own planet and they could see their suns.

None of them, not even their foremost astronomers, had ever imagined that there was much more to the universe.

When the Universal Law of Gravitation predicts an eclipse, the greatest danger to the minds of the people of Kalgash seems to be the impending darkness. They have good reason to fear a prolonged period of darkness; even a few minutes in the dark can drive some of them insane, and even strong minds can be severely shaken by the experience. A group of scientists are fearful...