Terrans, and the rest of the pan-galactic organization known as the Ekumen (from "ecumenical," no doubt) know the planet of Gethen as "Winter." Here in New York, it's the regular kind of winter, and though we don't have -30 days, or dozens of words for the combinations of temperature and wind, or giant ice sheets, reading about this frozen world felt very of the right moment. The Ekumen's envoy, Genly Ai, is never able to adjust to the bitter weather, which for Gethenians is merely a fact of life.
But the Gethenians pose far bigger challenges for Ai, as far as acclimation goes. The Gethenians are the only race in the universe that don't share our typical notions of gender. Instead of being split into male and female, the Gethenians are all one gender. Once a month they go into a kind of estrus called kemmer, in which they are compelled to copulate with another Gethenian, and through sexual touching, one Gethenian basically sprouts male genitalia and the other female genitalia. In this way Gethenians can either bear children or, for lack of a better word, "father" them. Ai is amused, for example, when the king of the nation of Karhide announces that he is pregnant.
The Left Hand of Darkness is everything that I was hoping Ann Leckie's Ancillary Justice would be: a thoughtful meditation on the contours of sex and gender by way of speculative fiction. The kemmer process bears its weight on Gethenian culture, in the same way that sex bears its weight on ours. Or, it might be better to say that Gethenian culture is defined by the absence of the sexual impulse and the lack of a gender-based dualism:
Consider: A child has no psycho-sexual relationship to his mother and father. There is no myth of Oedipus on Winter.
Consider: There is no unconsenting sex, no rape. As with most mammals other than man, coitus can be performed only by mutual invitation and consent; otherwise it is not possible. Seduction certainly is possible, but it must have to be awfully well timed.
Consider: There is no division of humanity into strong and weak halves, protective/protected, dominant/submissive, owner/chattel, active/passive. In fact the whole tendency to dualism that pervades human thinking may be found to be lessened, or changed, on Winter.
Ai's task is to convince the various nations of Gethen to join the Ekumen, a loose collective of planets who share their knowledge with each other. The challenge, of course, is that Ai has difficulty communicating with Gethenians because they are so different from him, and vice versa. The king, having granted Ai an audience, wants to know if it's true that he's a "pervert" who's basically in kemmer all the time. How do you convince a people to join you if you can barely see eye to eye about the basic structures of human life?
Ai gets caught up in some international intrigue between Karhide and its neighbor and rival, Orgoreyn. (In this way The Left Hand of Darkness does something rare in science fiction: it conceives of a planet not as a single cultural and political bloc, like most books do as a matter of convenience, but as a collection of nation-states like our own. Le Guin's worldbuilding is especially impressive when you realize that she's thought out not just the way that the absence of gender affects one culture, but two.) He ends up throwing his lot in with an exiled Karhidish nobleman, Estraven, whom he does not trust, but they end up having to endure an eight-hundred mile march across a frozen ice sheet to escape from their captors in Orgoreyn. It's during this journey that Ai learns to see through the eyes of his companion and vice versa, even coming close to falling in love with him, or her, or however you want to say it.
Like Orson Scott Card's Ender books, The Left Hand of Darkness is really about empathy: the difficulty, but necessity, of looking through eyes that are not your own, and recognizing a common humanity. Unlike Card, it seems that Le Guin was exactly the kind of person who put those difficult principles into practice. The Left Hand of Darkness is as gripping as it is thought-provoking, and all the encomia for it that appeared after Le Guin's recent death are richly deserved.