The Dark Forest

In a cemetery, Luo Ji meets with Ye Wenjie, a former leader of the Earth-Trisolaris Organization (a human group that is pro-Trisolaran). During that meeting, Ye Wenjie tells Luo Ji the foundational principles of what she calls cosmic sociology. At the time, Luo Ji isn’t aware of the significance of those principles.

The novel then flashes forward in time to year 3 of the Crisis Era, which is the third year after humans learn of the existence and the pending arrival of an alien race known as the Trisolarans, which will occur in roughly 400 years. In year 3, naval officers Zhang Beihai and Wu Yue are named to the newly formed Chinese space force. They’ll be in charge of designing a 400-year plan to try and defeat the Trisolarans. At this point, many people, including Wu Yue, believe that humans have no chance of defeating the Trisolarans because the Trisolarans are much more technologically advanced. Zhang Beihai ultimately calls out Wu Yue for his defeatist attitude in front of the other members of the space force, which leads Wu Yue to quit the military. In contrast, Zhang Beihai is a triumphalist who forcefully proclaims that humans will certainly defeat the Trisolarans when the time comes.

Meanwhile, Luo Ji wakes up in a hotel room with a woman whose name he can’t remember. The two get into an argument and decide to break up. As they’re leaving the hotel, a car swerves, hitting the woman and killing her. It narrowly misses Luo Ji, who is knocked out in the process. When Luo Ji regains consciousness, he’s in a basement bunker with a strange man named Shi Qiang. Shi Qiang escorts Luo Ji to an airport and ultimately to the UN building in New York City. Luo Ji is then brought to a meeting where he’s shocked when he learns that he’s been named one of four Wallfacers. As part of the global, UN-sanctioned Wallfacer Project, Wallfacers are given free rein to use the world’s resources as they see fit to try and devise a strategy to defeat or neutralize the Trisolarans. Wallfacers are especially encouraged to use deceit or deception to achieve those aims, as the Trisolarans have difficulty deciphering deception.

Luo Ji doesn’t understand why he has been chosen to be a Wallfacer and isn’t interested in the role. Using the powers granted to him, he moves into a lavish estate in the countryside and focuses on enjoying life. It doesn’t take long, though, for him to become lonely. To Shi Qiang, who is now in charge of Luo Ji’s security detail, Luo Ji describes the woman of his dreams before asking Shi Qiang to find her. Shi Qiang returns later with Zhuang Yan, a recent art school graduate. Luo Ji and Zhuang Yan fall in love, and Luo Ji couldn’t be happier. He continues to avoid working on the Wallfacer Project. The other three Wallfacers, on the other hand, diligently pursue their projects and meet regularly with the overseeing body, the Planetary Defense Council (PDC), to keep the PDC apprised of their progress.

Luo Ji and Zhuang Yan have a daughter, Xia Xia, and spend several happy years together. One day, Luo Ji wakes up and realizes that Zhuang Yan and Xia Xia are gone. General Secretary Say, the General Secretary of the UN, explains that Zhuang Yan and Xia Xia have been put into hibernation and will remain asleep until the Doomsday Battle (the day in approximately 400 years when humans will face off with the Trisolarans). If Luo Ji wants to see them again and to ensure that they are safe, then he must begin earnestly working on his Wallfacer Project and hope that it succeeds.

In response, Luo Ji begins working. He uses the pieces of information that Ye Wenjie gave him about cosmic sociology to put together a theory of how to combat the Trisolarans. Using that theory, he sends what he calls a “spell” into space aimed at a star about 50 lightyears away. He says there’s nothing more he can do until he finds out if his message reached anyone, so he enters hibernation. After he sends his “spell,” the Trisolarans send a battalion of probes that is set to reach Earth much sooner than the main Trisolaran fleet.

Luo Ji is awakened 200 years later. He quickly realizes that society has undergone significant transformations, and technological advancement has proceeded exponentially. Most people now live in technologically-responsive underground cities, where the mood among the general public is one of unalloyed optimism. People now believe that because humans possess such advanced technology, the Trisolarans will be forced to enter peace negotiations to avoid being destroyed by humans. No one thinks much of, or even remembers, the Wallfacer Project. Luo Ji meets up with Shi Qiang, who also entered into hibernation and has recently been reawakened. The two go to live on the surface of the Earth, where many people who arrived in the future through hibernation live.

The surface of the world has been turned into a vast desert through climate change. One day, a man comes to find Luo Ji and tells him he’s there to take him to the final Wallfacer meeting. By now, one of the original Wallfacers, Tyler, has died by suicide. That happened after his original plan was exposed by the ETO. A second Wallfacer, Rey Diaz, was killed after the ETO also exposed his plan, and people took offense because that plan threatened to destroy humanity. Luo Ji and a man named Hines are the only remaining Wallfacers. At the meeting, they learn that the project will now be formally terminated.

Meanwhile, Zhang Beihai has also recently reawakened from hibernation. Because he has been known as a devoted believer in humans’ inevitable triumph over the Trisolarans, he’s appointed to a ship where he’s supposed to help ferret out people who might still harbor defeatist attitudes. Once Zhang Beihai is granted control of the ship, though, he hijacks it and steers it far into space. He then reveals that he’s been a defeatist the whole time and had only been pretending to believe in the inevitability of human triumph to get to the point where he could execute his plan of stealing a ship, thereby giving some people a chance to survive in space after everyone on Earth is wiped out by the Trisolarans.

Around the same time that Zhang Beihai hijacks the ship, the first Trisolaran probe approaches Earth. At first, the humans think the probe might be a peace offering, in part because it’s so beautiful. That attitude doesn’t last long, though, as the Trisolaran probe destroys almost the entirety of Earth’s space fleet, which is over 1,000 ships, in less than an hour. People on Earth begin to panic.

During that panic, Luo Ji and Shi Qiang enter the city where they live and find a large crowd. They discover that the large crowd is waiting for Luo Ji, who is greeted as a kind of savior. People have just discovered that the star Luo Ji sent his “spell” to was destroyed.

Luo Ji then explains to Shi Qiang what has happened. He says that the destruction of the star confirms his theory that the universe is akin to a “dark forest” in which alien civilizations are represented by hunters. In that dark forest, communication is virtually impossible, and resources are scarce, which encourages an attack-first attitude or else one might be attacked. To avoid those kinds of situations, alien civilizations have tried to be silent and undetectable. Luo Ji tells Shi Qiang that when he sent out his “spell,” he broadcast the exact coordinates of a star into the universe. The star’s destruction is evidence that alien civilizations received Luo Ji’s transmissions, and at least one of those civilizations decided it would be easier to destroy the star than to investigate.

The Wallfacer Project is restarted, and Luo Ji is named as the only Wallfacer. Luo Ji says he can’t accomplish anything further because the Trisolarans have cut off the use of the sun as a transmitter, which is how Luo Ji sent his original message into space. The Wallfacer Project offers Luo Ji the opportunity to work on the Snow Project, an alternative project that aims to keep track of the Trisolaran fleet. Luo Ji throws himself into that work for three years. Over those three years, the public stops considering Luo Ji a savior and begins thinking of him as a fraud.

After three years have passed, Luo Ji walks to the cemetery where he once met Ye Wenjie. He begins digging a grave for himself. He then takes out a pistol from his pocket, aims it at his chest, and says that he wants to speak with the Trisolarans. Sophons—microscopic supercomputers the Trisolarans use to communicate with and surveil humans—appear and transmit text to Luo Ji. Luo Ji tells them that through part of the Snow Project, he’s carefully arranged bombs in space that will transmit the coordinates of the Trisolaran fleet if they’re detonated. He says the bombs receive a signal from a small device he’s wearing, and if he dies—that is, if he shoots himself in the chest—the bombs will go off, thereby notifying alien civilizations of the Trisolaran fleet’s location. That will also broadcast the Earth’s location, which means that both Earth and the Trisolarans will be destroyed if the signal is sent out. The Trisolarans admit defeat and acquiesce to Luo Ji’s demands that they call off their probes and change the course of their fleet to go away from Earth.

Afterward, Luo Ji is hailed as a hero, and Zhuang Yan and Xia Xia are reawakened. The Trisolarans and humans forge a tenuous peace, and the Trisolarans help humans advance their technology. Luo Ji hopes that maybe, through love, humans might be able to help illuminate the dark forest of the universe and make it safer for everyone.