This is a complex book ,and while it has its problems, it is one everyone should put on their "must read" list. It is one of a number of works in her Hainish Cycle, and it tells the story of a diplomat sent from the Ekumen (a loose confederation of worlds) to the planet Gethen (also called Winter) with the mission of convincing them to join the Ekumen. But his mission is very difficult because the culture of Gethen is unlike anything he has every seen. The people there are ambisexual, which means they can at different times be male or female. The essence of the novel is the developing relationship between Genly Ai, the Ekumen diplomat, and Estraven, a Gethenian politician who trusts him, and through their developing relationship we see how the culture and society of Gethen function.

This book was one of the first books in the genre of feminist science fiction, and kicked off quite a debate. One part of that is that while gender is so central to the novel, the two main characters, Ai and Estraven, are both male. Nonetheless, it is one the great works of science fiction and won both the Hugo and the Nebula Awards. In 1987 Locus ranked it second, after only Dune, among science fiction novels.