Returning to San Francisco after a long absence, Mary Ann Singleton reunites with the community of characters at 28 Barbary Lane.

100 years in the future, when the Earth has been abandoned due to radioactivity, the last surviving humans live on an ark orbiting the planet — but the ark won't last forever. So the repressive regime picks 100 expendable juvenile delinquents to send down to Earth to see if the planet is still habitable.