The Dark Forest (2008) by Cixin Liu is the second installment in his Remembrance of Earth’s Past trilogy. It is one of the most popular and critically acclaimed science fiction novels of the 21st century. Liu has become China’s most prominent science fiction writer and has enjoyed success both domestically and abroad. The novels’ settings focus on the past (1960s and 1970s), present, and future, respectively. In this series, Earth encounters an alien civilization in a nearby star system, the Trisolarans, whose solar system has three sun-like stars in an unstable system. In The Dark Forest, the Trisolarans have decide to destroy humanity to protect their own civilization.

Liu’s science fiction focuses on humanity’s technological advancement and the Remembrance of Earth’s Past trilogy explores the idea of human and non-human life elsewhere in the universe, and interactions between them. A dense and complex text, The Dark Forest focuses on conflict and how power imbalances and mutually assured destruction influence outcomes. The novel also draws on Chinese cultural influences which were the focus of the preceding instalment, The Three-Body Problem, particularly through an exploration of the Chinese Cultural Revolution (1967-1977).

A bestseller in China, the trilogy was translated into English for an international readership in 2015. Liu won the 2015 Hugo Award for Best Novel for The Three-Body Problem, the first novel in the series, and was nominated for the 2017 Hugo Award for Best Novel for Death’s End, the final book in the series. A 3-part BBC documentary series Rendezvous with the Future was released in 2022, exploring the theory and inspiration behind Liu’s science fiction.

This guide references the TOR Books 2015 edition, translated from Chinese by Joel Martinsen.

Content Warning: The source text and this guide contain material related to suicide and violent death.

Plot Summary

Humanity is in the Trisolar Crisis, set in an alternative present-day universe where Earth is interacting with an alien civilization, Trisolaris. The United Nations (UN) is seeking a way to survive the invasion of the Trisolaran fleet, which is expected to arrive in 400 years. The Trisolarans have deployed “sophons,” advanced subatomic devices that surveil all activity and communication on Earth and block humanity’s attempts to make technological advances that could help to defend against the attack. The sophons can communicate immediately with Trisolaris across space-time. The UN is also negotiating the activity of the Earth-Trisolaris Organization (ETO), a group of pro-Trisolaris humans who sabotage defense efforts.

In a flashback, Luo Ji remembers an interaction in The Three-Body Problem with Ye Wenjie (the protagonist of that book). Ye Wenjie is an anthropologist and key member of the ETO, and the person to contact the Trisolarans and encourage them to invade Earth. In the flashback, Ye Wenjie suggests that Luo Ji study “cosmic sociology,” a theory about the nature of civilization in the universe and how civilizations act toward each other.

It is Year Three of the Crisis Era and Zhang Beihai is reassigned from the Chinese Navy to the newly formed UN Space Force. Unlike his colleagues there, he pushes a view of triumphalism for the coming conflict. He holds this belief so firmly that he suggests his close colleague, Wu Yue, be dismissed for holding “defeatist” opinions.

In Beijing, Zhang Yuanchao and his neighbors Yang Jinwen and Miao Fuquan watch the news and discuss “Escapism,” a controversial notion that some of humanity should escape Earth and find survival elsewhere. This leads to an argument over who deserves to stay and go, resulting in Zhang Yuanchao investing money in the Escapist Fund.

Luo Ji is an astronomer leading a normal life until his lover is killed by a speeding car. He narrowly escapes with his life. He wakes up in a basement with Detective Shi Qiang. He is not told why he is being held but believes he is suspected of murder. Shi Qiang takes Luo Ji on a flight whose purpose and destination is unknown. While in flight, Luo Ji reminisces about a recurrent fantasy of a girl he had when he was younger. The plane lands at the UN and a new defense plan is revealed to Luo Ji: Four individuals are tasked with saving humanity. They will be given vast resources but hold their strategies inside their own heads in order to escape the sophon surveillance. The four people are Frederick Tyler, former US secretary of defense, Manuel Rey Diaz, former president of Venezuela, Bill Hines, neuroscientist and former EU president, and Luo Ji. This new plan is called the “Wallfacer Program.”

Luo Ji does not understand why he has been chosen. He rejects his role as a Wallfacer and leaves the UN, only to be shot at by a member of the ETO. He survives and reconsiders. He asks for a house be built for him far from society and plans to abuse his access to resources to live an easy life. Meanwhile, the Hubble II captures images of the Trisolaran fleet crossing a dust cloud, confirming its existence, and Zhang Beihai volunteers to work for the High-Tech Strategy division in Space Force.

ETO members gather in virtual reality to develop the “Wallbreaker Project.” These members are tasked with observing the Wallfacers and discerning their secret plans for defense against the Trisolarans. To the ETO, it appears that Tyler is making a mosquito-like swarm fleet, Rey Diaz is focusing on powerful hydrogen bombs, and Hines is seeking to develop the human brain.

Luo Ji continues abusing his powers, including asking Shi Qiang to find a version of his fantasy girl in real life. Shi Qiang finds a woman who meets this description, Zhuang Yan, and brings her to Luo Ji. Luo Ji tells her that she is integral to his Wallfacer plan and that she must become the happiest woman on the planet. She agrees to help him and asks to go to the Louvre, where they enjoy art and become familiar with each other.

Five years later, Luo Ji and Zhuang Yan are a married couple and have had a child. All of the three Wallfacers have been sabotaged by the Wallbreaker Program. Wallfacer Frederick Tyler’s Wallbreaker opposite appeared and exposed his plan to the world. The plan involved the destruction of the Space Fleet to gain the Trisolarans’ trust before betraying them. The public revelation of this plan resulted in Tyler being condemned by the international community. The distress of this led him to end his own life. The Wallfacer Hines has gone into hibernation.

Luo Ji finds out that the reason he was chosen as a Wallfacer was because the Trisolarans had attempted to assassinate him: They fear him for an unknown reason that suggests he has power against them. Luo Ji’s wife wants him to work on the Wallfacer Project. To force his hand, she puts herself and their child into hibernation (a kind of stasis) until the arrival of the Trisolaris fleet in 400 years. Her plan succeeds: After exploring the theory of “cosmic sociology,” Luo Ji has a private breakthrough in his work. Without explaining why, he broadcasts the location of a nearby star to the universe. He calls it a “spell” and will hibernate himself until the effects of his “spell” show. Shi Qiang and Zhang Beihai hibernate around this time too.

One-hundred-eighty-five years later, Luo Ji wakes from hibernation in a future Beijing, an advanced and prosperous society. Humanity has developed a strong Space Fleet and the Wallfacers Program has been terminated in the face of a what’s now considered a certain human victory. Shi Qiang, also awoken, investigates multiple attempts on Luo Ji’s life, discovering that a virus named Killer 5.2 from the ETO is trying to kill Luo Ji. Luo Ji follows Shi Qiang to the surface, where technology cannot harm him.

The Wallfacer Hines wakes from hibernation and discovers that his wife and scientific partner is his Wallbreaker. She reveals she has been “imprinting” soldiers with a sense of defeatism and that these soldiers could still be active in the UN fleet.

Zhang Beihai awakens and is tasked with finding these pessimistic “imprinted” soldiers. He takes command of a fleet ship Natural Selection and hijacks it, sending it into deep space toward a distant star. He reveals that he has always been an Escapist and sees humanity’s only chance at survival as flight. Simultaneously, a Trisolar probe arrives in the solar system. Humanity believes that it is a peace offering and the entire Space Fleet moves to intercept it. The probe, a perfectly smooth metal droplet, destroys the entire fleet in a matter of minutes.

With the Space Fleet destroyed, humanity falls into chaos. In the outer parts of the solar system, Zhang Beihai’s ship and the four pursuing him become their own independent human civilization. As their journey lengthens, and the darkness of space deepens, the captains of the ships realize that there are not enough resources for all to survive. The ships attack each other, leaving only one ship with a living crew. This ship, Blue Space, harvests fuel and resources from the other ships and makes off.

Luo Ji’s “spell” to broadcast the distant star’s location has led to it being destroyed by an unknown civilization in deep space, as he has predicted. He is immediately reinstated to Wallfacer status. He explains the theory behind his experiment which he calls the “dark forest”: As life increases and resources are finite, civilizations are incentivized to destroy others when they discover them. The only defense to this, he argues, is to go unnoticed.

In response to this breakthrough, the Trisolarans have stationed a probe near Earth which jams any further interstellar communication. Luo Ji begins working on a new project called Snow Project. This seeks to use oil film and hydrogen bombs to create a dust cloud that will alert humanity to other probes’ arrivals. Luo Ji uses this to place the bombs in a pattern that, when detonated, interrupt the probe and allow a message to be sent from Earth via the sun. He hails Trisolaris and threatens them with mutually assured destruction: He will reveal the location of both civilizations unless they call off their invasion. The Trisolarans agree, and a new age of cooperation between Trisolarans and humans is on the horizon. Luo Ji is reunited with his family.