Death's End

Death’s End (2010) by Cixin Liu is the third and final installment of the Remembrance of Earth’s Past trilogy. It is the follow-up to The Three-Body Problem (2006) and The Dark Forest (2008). Death’s End follows aerospace engineer Cheng Xin across centuries as she navigates the Trisolaran Crisis, sparked by aliens from the planet Trisolaris planning to invade Earth after their own world becomes uninhabitable. The novel explores themes of The Fragility and Resilience of Humanity, Surviving Existential Threats, and The Weight of Responsibility.

Liu is the most prolific science fiction author in China and has won multiple awards for his many works; Death’s End was a finalist for the 2017 Hugo Award for Best Novel and the 2017 Locus Award for Best Science Fiction, and the trilogy has been adapted into a Netflix series.

This guide references the 2016 English paperback translation by Ken Liu published by TOR Books.

Content Warning: The source material refers to death by suicide.

Plot Summary

In the first two novels of the series, humans discover that a nearby star system’s occupants, the Trisolarans, are heading to Earth to conquer humanity and take the planet for themselves. They will arrive in 450 years. The Trisolarans rely on sophisticated technology—including multidimensional computers called sophons, which disrupt scientific progress on Earth, record all communication, and instantly broadcast everything they record back to the Trisolarans—and on several groups of human collaborators, who welcome the destruction of the human race. To prevent the takeover, Earth develops several strategies; the most important is the creation of the Wallfacers: Four humans given almost unlimited resources to execute whatever plans they come up against the Trisolarans, as long as the Wallfacers tell no one of the plans—sophons can overhear any conversation, but they cannot read minds.

One of the Wallfacers, Luo Ji, eventually arrives at a way to stave off the invasion: The Dark Forest Deterrence, which relies on mutually assured destruction. The deterrence assumes that there are many intelligent species in the universe but a finite amount of resources, so any species whose location becomes known will be destroyed by others. Luo Ji threatens to broadcast the location of the Trisolarans to the universe, thus exposing both them and the inhabitants of the Solar System to annihilation—the threat causes the Trisolarans to halt their invasion plans.

While the first two novels follow events chronologically, beginning in the near future and advancing several hundred years, the last novel covers events from the entire timeframe of the series.

Death’s End opens during the Fall of Constantinople in 1453 CE (a real historical event). A woman becomes a highly successful thief and assassin when she develops the ability to acquire small objects, including internal organs, from other people. Later, her powers are explained as the appearance of a four-dimensional fragment in the Solar System.

The novel flashes forward to the Crisis Era, in Earth’s near future (21st and 22nd centuries). After the discovery of the coming Trisolaran invasion, one of Earth’s proposed countermeasures is to send a probe to spy on the Trisolaran Fleet; putting a human inside the probe will make it interesting enough to the Trisolarans that they won’t immediately destroy it. Due to weight constraints, the probe can only contain a brain—the hope is that the Trisolarans will rebuild the rest of the body when they intercept the probe. Cheng Xin, an aeronautical engineer working on the project under head of Planetary Intelligence Agency Thomas Wade, suggests using a sail accelerated by nuclear explosions.

Engineer Yun Tianming, who is terminally ill, has loved Chen Xin since college. He uses a surprise windfall to buy her a star named DX3906. Before he dies, Cheng Xin convinces him to donate his brain to the probe. However, during the launch, the probe goes off course, leaving Yun Tianming to float through space forever. Cheng Xin and Wade hibernate into the future.

The novel flashes forward to the Dark Forest Deterrence Era (23rd century). After Luo Ji creates his deterrence strategy, which relies on a gravitational-wave communications system that could transmit the Trisolarans’ location universe-wide, he is named Swordholder—the one person who can decide to activate the system and thus doom not only the Trisolarans, but also humans in the Solar System.

Before Luo Ji’s deterrence was operational, two groups of spaceships fled the Earth. However, each group is now comprised of only one ship—Bronze Age and Blue Space—whose crews decided their best chance for survival was to kill the other crews for their resources. The Bronze Age returns to Earth; its crew is immediately tried for crimes against humanity.

Cheng Xin wakes from hibernation and learns that the star Yun Tianming gave her has habitable planets. The UN buys the planets and rents access to the star’s energy from her; she uses the profits to start Halo Group. Luo Ji is unpopular as Swordholder and soon to be replaced. Cheng Xin’s star has made her into a savior figure likely to be named the next Swordholder. Sophon, a graceful artificial intelligence (AI) android and ambassador made by the Trisolarans, also endorses Cheng Xin as Swordholder.

The second Cheng Xin accepts the position, the Trisolarans attack, destroying all of Earth’s communications systems with droplets—small, indestructible unmanned spaceships. Cheng Xin cannot bring herself to activate the Dark Forest Deterrence transmitters. Sophon confirms that the Trisolarans wanted her to be Swordholder because she would be too weak to doom their two worlds. The now warlike Sophon forces all humans to live in Australia in terrible conditions; the Trisolarans want as many humans to die before they arrive as possible.

Meanwhile, Blue Space, which has been warned by Bronze Age not to return to Earth, is pursued by Gravity, a ship that still has functioning dark forest broadcasting capabilities. Droplets are poised to attack them right after the Swordholder handover. However, Blue Space has found another four-dimensional fragment and has learned to use its powers. Blue Space obliterates the droplets and takes over Gravity; learning that the Earth has been conquered, the two crews broadcast the location of the Trisolarans (and thus also of Earth). On Earth, Sophon discovers the broadcast. The Great Resettlement to Australia ends and the Trisolaran fleet alters course to escape.

The novel flashes forward to the Broadcast Era (late 23rd century to early 24th century). Cheng Xin and the rest of the Earth witness the destruction of Trisolaris by a weapon called a photoid. It occurs much sooner than they anticipated, which means that photoid came from a nearby spaceship. Sophon tells Luo Ji and Cheng Xin that Trisolaris was destroyed quickly because the Trisolarans appeared dangerous. However, there is a way for Earth to show weakness and thus possibly prevent a strike. Sophon also reveals that they have Yun Tianming’s probe; he wants to meet with Cheng Xin.

Yun Tianming and Cheng Xin meet virtually under Trisolaran supervision, which means Yun Tianming cannot share any secrets he may have been able to learn. Instead, Yun Tianming tells Cheng Xin three fables and ends with a promise to meet at their star in the future.

Analyzing the fairytales for hidden meaning, Cheng Xin and astronomer AA realize that one story, in which a piece of soap propels an origami boat across a tub, is about curvature propulsion, which would make light-speed possible. Another story suggests reducing the speed of light in the Solar System, technologically isolating humanity. Humanity studies these ideas and a plan to create bunker space cities behind the outer planets of the Solar System, safe from a photoid attack on the Sun. However, when it becomes clear that only the rich will have the resources to escape such an attack, light-speed travel is outlawed. Wade convinces Cheng Xin to sign Halo over to him so that he can secretly develop light-speed ships. She agrees and hibernates.

The novel flashes forward into the Bunker Era (24th century). Humans have abandoned Earth and live in space cities. When Cheng Xin wakes, Wade shows her his progress on light-speed travel, as well as his anti-matter weapons. Each can destroy a space city, allowing Halo to defend its right to make the ships. She asks him to back down and he agrees. He is arrested and executed. Cheng Xin hibernates again.

When Cheng Xin and AA wake up in the bunker world decades later, an alien species has deduced that there must be intelligent life on Earth. They send a small, thin weapon that creates a two-dimensional plane that sucks everything into it. The exit velocity of the Solar System is the speed of light, and humanity is doomed. Cheng Xin and AA go to Pluto to meet Luo Ji. As the Solar System collapses, Luo Ji reveals that they are actually on a light-speed ship: Halo’s research continued in secret. They thus escape to Yun Tianming’s star.

It takes almost 300 years to reach the star, though for them it feels like eight days. They find two planets, Planet Blue and Planet Gray; on Planet Blue is Guan Yifan, a member of the crews of Gravity and Blue Space, which have now settled across the galaxy. Guan Yifan shows Cheng Xin death lines—traps alien ships have left that reduce the speed of light to zero. The traps capture Cheng Xin and Guan Yifan, who take 18 million years to return. On Planet Blue, they find a message on a stone pointing them toward a pocket universe left by Yun Tianming.

Inside the mini-universe, Sophon tells them they can stay until the next Big Bang. However, they learn that the universe cannot collapse and reform until all pocket universes return their mass to the main universe. They decide to re-enter the universe, leaving nothing but a miniature computer with records of Trisolaris and Earth, as well as a small orb with algae, water, and fish in it.