Moon follows Sam Bell, an astronaut assigned by Lunar Industries to a three-year mission mining Helium 3 on the moon, the earth's new energy source. As his contract comes to an end and Sam's health starts to deteriorate, painful headaches, hallucinations and a lack of focus lead to an almost fatal accident. While recuperating, Sam meets a younger, angrier version of himself, who claims to be there to fulfill the same three-year contract Sam started all those years ago.
