The film follows the story of Genly Ai, a human native of Terra, who is sent to the planet of Gethen as an envoy of the Ekumen, a loose confederation of planets. Ai's mission is to persuade the nations of Gethen to join the Ekumen, but he is stymied by a lack of understanding of their culture. Individuals on Gethen are ambisexual, with no fixed sex; this has a strong influence on the culture of the planet, and creates a barrier of understanding for Ai.