Sam Bell (Sam Rockwell) is an employee contracted by the company Lunar Industries to extract helium-3 from lunar soil for much-needed clean energy back on Earth, leaving behind his wife Tess, who is (at the time of his leaving) heavily pregnant with their daughter, Eve. He is stationed for three years at the largely automated "Sarang" (sarang means love in Korean) lunar base with only a robotic assistant named GERTY (voiced by Kevin Spacey) for company; a chronic communications satellite failure limits him to only occasional recorded transmissions to and from Earth as fixing the link is currently not among the top priorities of Lunar Industries. Two weeks before completing his contract, he begins to hallucinate, briefly seeing a teenage girl on the station. During a routine rover excursion to retrieve ready canisters of helium-3 from a harvesting machine, he sees the same girl standing on the lunar surface. Distracted, he crashes the rover into the harvester, losing internal atmosphere and switching in a hurry to the suit life support.
Sam awakens in the infirmary and GERTY tells him that he is recovering from injuries sustained in an accident. Sam's suspicion is aroused when he eavesdrops on a live communication between GERTY and Lunar Industries headquarters, and learns that GERTY will not allow him outside the base. A message from Lunar Industries executives informs him that a rescue crew is on the way, to repair the harvester and take him home. Sam sabotages a base gas pipe to convince GERTY to allow him outside to repair the fault. Once outside the base, Sam instead goes to investigate the damaged harvester, where he finds someone barely alive in the crashed rover: another Sam Bell, identical to himself......Get downloading!!!