A cargo spaceship, propelled by a photon engine with a large reflective mirror ("sail"), visits the Jupiter system to deliver cargo to a staffed science station on Amalthea. Damaged by meteorites, the spaceship falls into Jupiter but survives the pressure and floats in the dense atmosphere. The crew manage to work around the damaged mirror and start the main engine to escape Jupiter and finally reach Amalthea.

Roadside Picnic is set in the aftermath of an extraterrestrial event, the Visitation, which occurred simultaneously in several locations around the Earth over a two-day period. Neither the Visitors themselves nor their means of arrival or departure were ever seen by the local populations, who lived inside the relatively small areas, each a few square kilometers, of the six Visitation Zones. The Zones exhibit strange and dangerous phenomena that are not understood by humans and contain artifacts with inexplicable properties.