The novel begins with a scientist named Shevek getting aboard a space ship to leave his home planet Anarres to travel to the neighbor planet Urras. He's been in contact with the scientists from there and wants to go there in hopes of connecting the two worlds and researching more about his Theory of Simultaneity. When he arrives there he is surprised by the lush nature and many people, contrary to the desert-like Anarres.
The novel consists of two time periods being told one chapter after the other: the time after Shevek's arrival to Urras and the time from Shevek's childhood up until his decision to travel to Urras.
On Urras, Shevek naively trusts those who brought him there and gave him the award for his research up until he realizes their motives of having his theory to rule above rest of the universe. Seeing the truth he joins the anarchists of A-Io, who are followers of Odonianism, the philosophy of Odo, who is seen as a founder of the structure of Anarres. He escapes the Ieu Eun University where he is being held and joins them in protests which end up being shut down by the military and many people killed.
Shevek finally decides to go to the Embassy of Terra, Terra is another planet populated by humans/aliens, and makes a deal with the ambassador to broadcast and distribute his theory of Simultaneity to all the populated planets in exchange for returning home to Anarres.
The other plot-line shows Shevek's childhood, his growing interest in temporal science, and the life on Anarres where everyone is equal and there is no law other than individual consciousness and group effort. He ends up as a scientist and math teacher for Sabul, who is a hidden egoistic and uses everyone and everything for his hunger for power. Sabul accepts to publish Shevek's work only when he can be the co-author.
Shevek soon meets Takver with whom he decides to start a partnership, a version of marriage. They have two daughters together, Sadik and Pilun. Not long after Sadik is born, a devastating drought hits Anarres, and they are forced to separate for long four years. After they finally reunite Shevek and Takver decide to go with their own initiative to publish Shevek's work by themselves and with the help of their close friends.
Shevek becomes a member of the Syndicate, he's been communicating with the scientists on Urras, and they even awarded him with Ieu Eun award for his scientific discoveries. He has a few allies on Anarres as most of them consider him a traitor for working with Urras. Seeing that his family and those around him are endangered with being shunned from the society he decides that the best option for him would be to go to Urras to try to take down the wall and bring the worlds together.
In the final chapter Shevek is traveling back to Anarres on a Hainish ship, Hainish are another human civilization. One of the Hainishmen, Ketho, decides to join him back to Anarres. Shevek looks forward to returning home the same way he left it, with empty hands.
