People in the future live in a totalitarian society. A technician named THX 1138 lives a mundane life between work and taking a controlled consumption of drugs that the government uses to make puppets out of people. As THX is without drugs for the first time he has feelings for a woman and they start a secret relationship.

The film features a conversation between Lucas and Francis Ford Coppola, producer of THX 1138. They discuss Lucas' vision for the film, including his ideas about science fiction in general and in particular his concept of the "used future" which would famously feature in his film Star Wars. Intercut with this discussion is footage shot prior to the start of production of THX 1138 showing several of its actors having their heads shaved, a requirement for appearing in the film. In several cases the actors are shown being shaved in a public location. For example, Maggie McOmie is shaved outside the Palace of Fine Arts in San Francisco, while Robert Duvall watches a sporting event as his hair is cut off. Another actor, Marshall Efron, who would later play an insane man in the film, cut off his own hair and was filmed doing so in a bathtub.