In the year 2021, the moon is in the process of being colonized, and this new frontier is attracting a diverse group of people to settlements such as Moon City, Farside 5 and others.
Two such denizens of this rough and tumble lunar society are the notorious millionaire J. J. Hubbard and former-astronaut-turned-satellite-salvager Bill Kemp. The first man to set foot on Mars, Kemp has now left the Space Corporation because he wants to do space exploration whereas his former employer only wants to do commercial passenger flights to Mars and Venus (the first manned mission to Mercury has not yet been made since there is no compelling financial interest). When Hubbard hears of a small 6000-tonne asteroid made of pure sapphire that is orbiting close to the moon, he hires Kemp to capture it using Kemp's old Moon 02 space ferry and bring it down to the lunar farside although it would be against the law. However, Kemp has little choice since he has learned that his flight license soon will be revoked due to protests from the Corporation. Hubbard also reveals that he plans to use the sapphire as a rocket engine thermal insulator; he would build more powerful rockets capable of finally colonizing Mercury and the moons of Jupiter—for profit.
Meanwhile a young woman arrives looking for her brother, a miner working a distant patch of moonscape at Spectacle Crater on the lunar farside. Unfortunately, the trip from Moon City on the nearside would take six days by lunar buggy. Since Kemp could go there in 20 minutes using Moon 02, she convinces him to try to learn whether her brother is still alive. In doing so, Kemp learns more than he would like about some of Hubbard's schemes.
- The singer of the theme song is Julie Discoll, who is most famous for her version of Bob Dylan and Rick Danko's "This Wheel's On Fire". It was later used as the theme song for the British TV comedy Absolutely Fabulous.
- The stewardess in the buggy early in the film is the actress Carol Cleveland, who would later go on to co-star on the TV series Monty Python's Flying Circus and the subsequent films.
- It was released three months after the Apollo 11 moon landing. A reference to that event was added to the dialogue in post-production.
- The film was released as a double bill with When Dinosaurs Ruled the Earth (1970).