In the distant future, an overcrowded Earth relies on research conducted by scientists in remote stations across the solar system. Contact is maintained by spaceships shuttling between the stations and large orbiting space stations. Captain James is preparing to depart from one of these stations when he is murdered by Captain Benson (Keitel). Benson, who was rated "potentially unstable" on a mental exam, steals James' cargo ship and departs the station for a small, remote experimental hydroponics research station on Saturn's Tethys (moon). Arriving there, he finds the station run solely by Adam (Douglas) and his colleague and lover Alex (Fawcett). Adam, the younger Alex, and their dog, Sally, enjoy their isolation far from an overcrowded and troubled Earth. The couple have been on Saturn 3 for three years, but Alex has spent all her life in space, and knows little of the habits and mores of humans who live on Earth.