In 2035, Lunar Industries have made a fortune after an oil crisis by building a large lunar mining base on the Moon, called Sarang, and since then have been extracting a large amount of helium-3 back to Earth. The system is practically automated, but the company requires one person on the station to monitor and send back shipments of Helium-3 when needed. Consequently, Sam Bell is that sole employee who is serving out his 3 year contract on the moon. To save costs, workers stay up there for long periods in solitary confinement. With not another living soul on the moon, Sam occupies himself by talking to his plants, carving a miniature model of his town, and talking to computer with an emoticon personality named Gerty 3000. All he wants is to return to Earth to be with his wife Tess and their infant daughter Eve, who was born just prior to his leaving for this job.
GERTY does everything in his power to empathize with and protect the Sam clones, even to the extent of keeping the fact that two are awake at the same time from the corporation. Nevertheless, he cannot satisfy the clones’ basic human need for meaningful contact with another human being.
As he’s nearing the end of his three-year tour of duty, Sam crashes one of the company’s harvesters and wakes up in the infirmary to find he has a doppelganger. Is he hallucinating or is he losing the plot after three years isolated from human contact?
Gerty informs Sam that a rescue team has been deployed from Earth to fix the harvester and Sam is to remain in the base.
Sam is suspicious, leaves the base anyway, and opens the hatch of the crashed harvester to find another Sam. Things don’t add up. He asks Gerty what is going on and Gerty replies that the other Sam is Sam Bell. The Sams are clones. Every three years, a new one is awakened and imprinted with the same memories.
Eventually, the two Sams discover the terrible truth: they are in actuality clones, created by Lunar Industries for cheap labor.
The two clones put their heads together and come up with a plan. The first Sam climbs back into the harvester while the newer Sam launches back to Earth just as the rescue team arrive. The credits roll as a voiceover of a radio show announces that Sam Bell will be testifying against Lunar Industries over the cloning controversy.