Cibola Burn

The fourth installment in The Expanse science fiction series, the novel takes place in a future where humanity has spread across the solar system and a network of alien ring gates has recently opened passages to over a thousand new star systems. On the planet Ilus (also called New Terra), the first human settlement beyond the gates is spiraling toward violence, and the crew of the independent ship Rocinante is sent to mediate.

The story opens with Bobbie Draper, a former Martian Marine working in veteran's outreach, observing the early consequences of the ring gates. Mars is losing population as people eye the new worlds, and her family argues over whether the planet's centuries-long terraforming project has become obsolete. A breaking news alert interrupts: tragedy has struck on New Terra.

On Ilus, Basia Merton, a former welder and refugee from Ganymede, one of Jupiter's moons, plants homemade bombs under a landing pad built by Royal Charter Energy (RCE), a UN-chartered corporation. Driven by grief over losing his son Katoa during a previous conflict on Ganymede and by fury at what he sees as a corporate invasion, Basia tries to disarm the bombs when RCE's ship, the Edward Israel, arrives ahead of schedule and drops its shuttle. He can only remove one of four detonators. The remaining charges detonate, debris strikes the shuttle, and it crashes, killing the provisional governor and roughly a dozen others.

Elvi Okoye, an RCE exobiologist, survives the crash. The colonists of First Landing provide medical aid, led by Doctor Lucia Merton, Basia's wife, though sabotage is the most likely explanation for the explosion. Aboard the Edward Israel in orbit, security chief Adolphus Murtry dispatches a ground team and learns that the UN and the Outer Planets Alliance (OPA) are sending a mediator.

That mediator is James Holden, captain of the Rocinante. For two years, the ghost of Detective Miller, a construct generated by the protomolecule, an alien technology of immense power, has appeared to Holden, urging him to investigate the worlds beyond the gates. OPA leader Fred Johnson and UN official Chrisjen Avasarala jointly propose Holden for the job. Miller pushes Holden to accept so the construct can investigate whatever destroyed the civilization that built the protomolecule. Holden learns that Miller's presence is possible because a small, non-living protomolecule node was placed on the Rocinante during a previous encounter, allowing the alien network to project the construct. Holden's crew agrees to the mission: XO Naomi Nagata, mechanic Amos Burton, and pilot Alex Kamal. Naomi, whose Belter physiology cannot handle Ilus's above-Earth gravity, will remain in orbit.

Tensions deepen on Ilus. A resistance cell led by a colonist named Coop pressures Basia into continued action against RCE. Elvi discovers hidden explosives in alien ruins outside town and reports the find to RCE security. When a surveillance team is posted at the ruins, Coop leads the cell in a lethal ambush, killing all five RCE personnel. Basia is present but his weapon never fires. Meanwhile, Murtry's security officer Dimitri Havelock, aboard the Edward Israel, follows orders to weaponize the ship's remaining shuttle by stripping its reactor's safety overrides to create a remote-controlled bomb.

Holden arrives to find a standoff. When Coop verbally threatens Murtry in front of a crowd, Murtry shoots him dead. Holden begins mediation between Carol Chiwewe, the colony's elected coordinator, and Murtry, reaching a fragile compromise over mining operations. Events escalate on multiple fronts: Holden's team discovers a massive alien mechanism on the surface, and Miller reveals a mysterious void in the planetary network that may be connected to whatever destroyed the alien builders. Basia, horrified by the resistance cell's plans to kill all remaining RCE personnel, warns Holden. Murtry, who has been bugging the entire town, already knows. He orders a preemptive strike that destroys the cell, killing several colonists.

Holden places Basia in protective custody aboard the Rocinante. Naomi discovers the Israel's weaponized shuttle and attempts an EVA to disable it, but Havelock's militia captures her. Alex locks the Rocinante's rail gun on the Israel's reactor, demanding Naomi's release.

A planetary catastrophe then dwarfs the human conflict. An alien power plant detonates beneath a distant island chain, sending hurricane-force winds around the planet. Holden evacuates everyone into the alien ruins, which withstand winds exceeding 370 kph. First Landing is obliterated. The explosion activates an ancient defense network that disables fusion reactors on all three ships in orbit, leaving them on battery power with decaying orbits. The colonists' ore ship, the Barbapiccola, faces atmospheric entry within days.

Inside the ruins, an alien microorganism carried in the rainwater begins colonizing everyone's eyes, causing progressive blindness. Holden alone is immune because his daily anti-cancer medication, taken for chronic radiation damage, also kills the fast-dividing alien organism. Elvi identifies this connection, and Holden donates his supply to treat the colonists, accepting the personal risk of developing new tumors.

In orbit, Havelock grows disillusioned with Murtry's willingness to let people die for corporate precedent. He uses nonlethal weapons to disable his own militia, frees Naomi, and escapes with her and Basia to the Rocinante. Naomi devises an audacious rescue for the Barbapiccola: she programs the rail gun to fire slugs as a makeshift thruster, using recoil to push both ships, connected by a tether Basia welds into place, into a higher orbit. The Israel's militia attacks with improvised missiles, severing the tether and wounding Havelock. With the Barbapiccola's orbit irrecoverable, Basia helps evacuate its crew using improvised life-support pods. His daughter Felcia is in the last pod. The Barbapiccola burns up in the atmosphere, but all hands are saved.

On the surface, Holden descends into an underground alien transit network guided by Miller, who inhabits a massive alien robot. Miller explains that Ilus was designed to process rare minerals and beam energy across a network of worlds. Murtry pursues Holden, accompanied by RCE security officer Chandra Wei. Elvi, Amos, and RCE geologist Fayez Sarkis follow in a second vehicle. At the alien structure, Murtry shoots Amos from behind; in the crossfire, Wei is killed. Fayez attacks Murtry to buy Elvi time to run deeper toward Holden. Holden confronts Murtry on a narrow bridge, rejects his philosophy that frontier conquest requires ruthless violence, and shoots him three times, wounding but not killing him. He drags Murtry to safety for eventual prosecution.

Elvi reaches the nerve center with Miller. At its heart floats the dead spot: a pulsing darkness Elvi can perceive but Miller cannot. Miller connects himself to the entire planetary network and asks Elvi to carry his core component into the void, using whatever killed the alien builders to shut everything down, including himself. When dormant machines activate and attack, Elvi fights her way through, extracts Miller's core from his destroyed robot body, and carries it into the dead spot. She experiences a profound dissolution and reassembly at the molecular level, then emerges alive. Every alien artifact on the planet goes silent, and fusion reactors function again.

With power restored, the immediate crisis ends. New First Landing begins construction with RCE and colonists working side by side. Holden chooses not to prosecute Basia, who reunites with his family. Holden removes the protomolecule node from the Rocinante and ejects it into Ilus's sun, a final farewell to Miller. Murtry is confined in the ship's med bay for delivery to the UN for prosecution.

In an epilogue, Avasarala reveals to Bobbie that Holden's success has accelerated a crisis: a thousand habitable worlds make Mars's terraforming obsolete, driving population flight and eventual state failure. The danger is Mars's military arsenal, including thousands of nuclear warheads and advanced warships, which will be vulnerable when Mars's government collapses. Avasarala recruits Bobbie for an unspecified role in managing this threat, setting the stage for the next volume.