On the moon, one man monitors automated mining. He is coming to the end of a three-year stint and is shortly due to be taken back to earth. When he leaves his base to check on a problem, he has an accident from which he can not be rescued as there is no-one to rescue him. He then 'wakes up' back at the base and doesn't remember the accident.
What happens next is pretty obvious to anyone with even the slightest familiarity with SF, including the nature of the individual who wakes up. You can work it out without too much difficulty from the four sentence synopsis of the first 30 minutes. But, I'm going to do it for you.