In the 23rd century, everybody lives under a giant dome made of glass, where they are free to do as they please as long as they are under 30 years old. Everyone who turns 30 has to enter the so-called Carousel, where they are "renewed", killed. The group of the "runners" in this society object to this and what to be older than 30. A sandman, as the policemen in the city are called, is told to infiltrate the runners. While doing this, the sandman leaves the dome and learns that human beings can be much older than 30. Returning to the dome, he is arrested but can eventually destroy the dome.