It’s the height of the Chinese Cultural Revolution, and for college student Ye Wenjie, the world is falling apart. Her father, a theoretical physics professor named Ye Zhetai, has been tortured to death for his allegedly anti-Communist beliefs, and her mother, Shao Lin, was among his torturers.
A few years later, Ye Wenjie has been sent to a Mongolian labor camp, where she spends her days cutting down trees. When she befriends reporter Bai Mulin, Ye learns that humans are rapidly destroying Earth’s environment. Bai wants to write to the Chinese government and urge them to slow the rate of their deforestation, and Ye offers to transcribe the letter for him. However, the letter backfires, drawing the government’s ire, and a panicked Bai frames Ye for the entire thing.
Ye expects to be tortured for the letter, but to her surprise, she instead is brought to a mysterious mountain called Radar Peak. The peak, named for the giant antenna on top of it, is home to the Red Coast military base. At Red Coast, scientist Yang Weining, one of Ye’s father’s former students, greets her. Yang explains that if Ye works as a researcher on Radar Peak, she will be spared punishment—but once she enters the military base, she can never leave it. Without hesitation, Ye joins Red Coast.
The story jumps four decades. Wang Miao, an expert in a brand-new technology known as nanomaterial, has recently received an invitation to join a secretive group called the Frontiers of Science. Soon after, Wang is summoned to China’s Battle Command Center. To his surprise, he learns that all of the nations of the world are working together to fend off some outside threat. Though the nature of the danger remains unclear, it has something to do with a rash of recent suicides in the scientific community. After being pushed by a rude police officer named Shi Qiang—and after learning that a respected physicist called Yang Dong has taken her own life—Wang agrees to join the Frontiers as a spy.
The next day, Wang begins to see an inexplicable countdown behind his eyelids. At first, Wang believes he is hallucinating, but gradually he realizes that the numbers he is seeing really do exist—he just has no clue what happens at the end of the countdown. In search of answers, Wang visits Shen Yufei, the physicist who introduced him to the Frontiers of Science. At Shen’s house, Wang meets her husband Wei Cheng; he also notices that Shen is playing a virtual reality game called Three-Body. Shen correctly informs Wang that if he stops working on nanomaterials, the countdown will cease.
Now even more baffled, Wang logs on to the Three-Body website. In the game, players are transported to other eras in history, from China’s Warring States period to Medieval Europe. But in the game world, the sun does not rise and set consistently. Instead, time is separated into Stable Eras (when the sun is predictable) and Chaotic Eras, when the sun might vanish for weeks or suddenly get so close to Earth that everything is scorched. Wang learns that the goal of Three-Body is to predict the sun’s movement by correctly understanding the game planet’s solar system.
Back in the real world, Wang continues to seek answers, befriending Shi Qiang and meeting with Yang Dong’s mother—who is none other than Ye Wenjie. Ye reveals to Wang that the true purpose of Red Coast Base was to try to make contact with alien life, but she claims that no such contact was ever achieved, so the base was shut down.
Wang logs in to Three-Body again. Having studied the sun’s movement and having tracked the flying stars that sometimes show up in the night sky, Wang concludes that the game’s planet has three suns. However, because each of the suns has its own gravity, “their movements are unpredictable—the three-body problem.”
The next day, Wang and Shi meet with Wei Cheng. Wei tells his life story, explaining that he accidentally came up with a brilliant method of solving the three-body problem. Now, a famous environmentalist named Pan Han is threatening him: Pan has told Wei that he must stop trying to solve the problem or face certain death. Sure enough, when Wang and Shi arrive at Wei’s house, they discover that Pan murdered Shen.
Through all of this, Wang continues to log into the virtual reality game. He learns that the planet of Three-Body (now known as Trisolaris) is in constant danger of being swallowed by one of its suns. The Trisolarans have therefore decided to abandon their planet and search for another home in the galaxy.
At Shi’s urging, Wang attends several meet-ups of Three-Body players. Over the course of these meetings, Wang is shocked to learn that Trisolaris is real, and that its residents are actually coming to Earth. Even more surprising, however, is the fact that Ye Wenjie leads a society known as the Earth-Trisolaris Organization (ETO), which aims to help these aliens in their conquest. The ETO is divided into two factions: Adventists, who believe that the Trisolarans should completely destroy humanity, and Redemptionists, who believe that humans and Trisolarans can work together to form a better world.
Ye explains that at Red Coast, she had secretly sent a message into space—and had received a reply from a Trisolaran pacifist known only as listener 1379. Though the listener had warned Ye Wenjie that if she replied, the Trisolarans would be able to track her location and invade Earth, Ye had replied anyway. After all, human beings had killed her father; what did she owe humanity?
Ye then explains how she had partnered with Mike Evans, the son of an American oil baron, to form the ETO. But in recent years, Evans has split off, hoarding communication with the Trisolarans on a special ship known as Judgment Day. At Shi’s suggestion, the generals of the Battle Command Center agree they will intercept Evans’s ship at the Panama canal—and then slaughter the ship’s crew, using a net made out of Wang’s nanomaterials (a project they call Operation Guzheng).
The operation is successful, and the generals learn the reality of the Trisolaran threat. The Trisolarans will arrive on Earth in 450 years; to ensure that humans cannot fight back, the Trisolarans have figured out a way to cease all human scientific progress. Specifically, scientists on Trisolaris were able to create four super-intelligent protons known as sophons, which could jam up all the particle accelerators on Earth. These faulty machines then created theoretical chaos and thus prompted all the scientists’ suicides.
Before Wang can lose hope entirely, Shi takes him to a small, locust-infested town. Shi points out that though humans have better technology than locusts, locusts have nevertheless survived human attacks for thousands of years. Wang resolves to get back to work.
