The novel takes place on the planet Gethen or as also it is called Winter, which main peculiarity is cold climate. The main feature of the inhabitants of this planet is a sequential hermaphroditism. The adult inhabitant of Gethen has a sexual cycle with the length of 1 month or 26 days. Within 21-22 days, the inhabitant is sterile, for another time, he is in a phase of the fertility. If during this time he finds a sexual partner, one of the partners will plays a male role and the other will play a female one. If the conception happens, the effect of hormones is stored for future mothers during the pregnancy.
The story is recounted by Genly Ai and Estraven in turn. Henry Ai prepares to meet Estraven. Estraven gives him a piece of advice to be courage, but Ai doesn’t believe and he cannot decide whether to treat Estraven as a man or a woman.
Argaven refuses Karhide to enter to the whole habitable globe, dispenses Estraven form the portfolio and gives the order to arrest and execute him, but he grants a delay that Estraven will be able to escape to Orgoreyn.
Genly gets to know about Estraven’s expulsion, but it doesn’t matter. He travels with Karhide and stops at the castle, which is a home of monks, who can provide the accurate and correct answer to any question. Genly asks the oracle if he will be a member of the whole habitable globe. Oracle says “yes”. Genly finds that Argaven is pregnant.
Meanwhile, Estraven leaves Karhide. Along the way, his ex-partner Estre finds him. Estre tries to give Estraven money, being exposed to danger. Estraven doesn’t want to expose Estre to danger and feels his fault for the indifferent love to Estre. He decides to go to Orgoreyn.
Genly Ai submits an application to do to Orgoreyn. Estre visits him and gives a huge sum of money for Estraven. Genly gives Estraven money, but he doesn’t trust him and tries to avoid the meeting with Estre. Estraven understands that Genly is in danger. Karhide and Orgoreyn prepare for a war.
The secret police decide to arrest Genly as a spy and sends him to a concentration camp. When Estraven gets to know about it, he decides to rescue Genly and send him back to Karhide. In their conditions, it means that they will need to go together through the glacier in the winter. Estraven kidnaps him and takes away to safety. The war begins between Karhide and Orgoreyn.
Genly begins to trust Estraven, but he doesn’t understand his motives. Genly offers Estraven to teach him the language of thoughts, which gives no opportunity to lie. Genly speaks this langue and he is positive of his truthfulness. Genly gives him few lessons. During lessons Estraven hears the voice of Genly as the voice of his lost brother and lover Arek. Genly and Estraven become closer, but Estraven’s character is a mystery for Genly.
Estraven and Genly together go through the glacier. Estraven advises Genly to call for help other members of the mission who are on a spaceship. In this case, Argaven will be forced to hand in application to join the whole habitable globe. Genly agrees.
Estraven leads Genly up to his friend. Henley sends a signal to the ship. Estraven’s friend transmits the information about Estraven to people. Estraven knows about it and tries to cross the border with Orgoreyn. Border guards arrest Genly and kill Orgoreyn.
As Estraven predicts, driven into a corner Argaven agrees to have a diplomatic meeting with representatives of the whole habitable globe, but fails to rehabilitate Estraven. Genly doesn’t insist. He visits Estraven’s clan to pass his diaries there and talk about the last months of his life. He meets with mother and Estraven’s child and brother Arek.