Sam Bell (Sam Rockwell) is an astronaut who is nearing the end of his three year stint on the moon. He is the sole inhabitant of the lunar base, which monitors all of the remote mining on the surface. A new form of energy, from moon rocks, supplies the majority of the power to Earth. His only companion is the computer/robot Gerty (voice of Kevin Spacey). He's anxious to get back to his beautiful wife and young daughter. But he's beginning to hallucinate and starts seeing people. When he goes out to inspect a huge mining vehicle in his rover he gets distracted and crashes into the machinery. Then, he awakens in the base's medical facility. Gerty explains that he was in an accident and that he must remain inside until he recovers. For some reason this doesn't sit right with Sam and he manages to get outside. He goes to where he crashed the vehicle and finds a body inside--a body that looks exactly like him.
At first we're not too sure if he's losing his mind or not but this doppelganger seems to be entirely real. MOON has that weird feel of SPACE 1999 and is a fascinating examination of what it is to be isolated and alone. It's also one of the best science-fiction movies I've seen in a good long while. Highly recommended.