Sam Bell has a contract a three year contract with Lunar Industries. He is the only employee based at their lunar station which is the moon, his job is to harvest periodically rocket back to the supplies of helium-3, to the earth. Helium used as electricity and a fuel on Earth. Although there is no direct communication link available between the lunar station and Earth, Sam Bell could only communicate with Gerty, a robot that keeps his company while he stayed there. It has been almost three years and he is able to go home in two weeks, it would be his last harvest for helium when he encountered an accident.
It has been awhile; he lied in his truck and was lucky that someone has found him there unconscious. When he woke up, he found out that the one who saved him is totally look like him. The two Sams were confused, they thought of whom is real and who is not. They bluntly said that they were not the clone. They asked Gerty the robot about it, that can’t tell them what’s going on, the one want to go home but he feels like he will die in due time. Later, they agreed to find out the truth, they both work hard what was happening then, they must report it to the government but how could they do that when the communication to the Earth has been blocked. They convinced Gerty to help them, Gerty told them to reprogram him when they finish their mission to escape.
The whole synopsis is here.