Juliette Andromeda Mao is seized when unknown, armored boarders take the Scopuli. Locked away on the attackers’ ship, she later forces her way free and finds engineering overgrown by a wet, pulsing mass that has absorbed crew—including her captain, whose embedded head pleads for help. Her discovery is the silent spark beneath everything that follows.

Near Saturn, the ice hauler Canterbury intercepts a verified distress beacon from a Martian light freighter: Scopuli. Executive Officer James Holden leads a shuttle team to investigate and finds a ship vented by shaped charges, a correctly shut down reactor, no bodies, and a fake, battery-powered transmitter—a lure. As they withdraw, a stealth warship fires nuclear torpedoes and vaporizes the Canterbury. Reeling, Holden compiles every scrap of sensor data and broadcasts a public accusation that Martian hardware and stealth tech were used, throwing gasoline onto Belt–Mars tensions.

On Ceres, Detective Josephus Miller is assigned off the books to retrieve Julie Mao for her wealthy Luna family. While he notes an odd retreat among the station’s gangs and OPA cells, Holden’s broadcast turns Ceres volatile. Miller calms his Earther partner Havelock, then confronts riots, missing riot gear, and OPA agitprop that erode Star Helix’s legitimacy. His search of Julie’s apartment reveals discipline, OPA leanings, and a chilling, pre-crisis message from her father urging her to flee the Belt—hinting at foreknowledge.

The Martian battleship Donnager takes Holden’s crew aboard to debrief, but six silent ships close in. In a brutal engagement that shreds assumptions about capital-ship invulnerability, a gauss round decapitates medic Shed Garvey and boarders seize the ship. Holden, Naomi Nagata, Alex Kamal, and Amos Burton flee with a dying marine aboard the corvette Tachi as the Donnager is destroyed. Cutting their transponder, they accept aid from OPA leader Fred Johnson on Tycho Station, spoof a new identity as Rocinante, and become independent contractors under Fred’s political protection.

Back on Ceres, Miller pushes Julie’s case against orders, tracks a new extortion ring wearing OPA colors, and watches the old syndicates vanish. Anderson Dawes pressures him to drop the search and reveals Julie was on the Scopuli. Fired as OPA influence replaces UN oversight, Miller follows a hunch through docking logs to a suspicious “gas hauler” he suspects is Holden’s ship and redirects to Eros, where that ship’s next lead points.

On Eros, Holden’s crew climbs to a flophouse seeking “Lionel Polanski,” a paper owner of the Scopuli, and is ambushed by a professional hit squad. A Belter tail helps turn the fight and introduces himself as Miller. Together they breach the target room and find Julie Mao dead in the shower, her body grotesquely transformed by an unknown, radiation-hungry organism. Her hand terminal reveals she escaped the Scopuli, believed she carried a “Phoebe bug,” and left a rock coordinate. They conclude she died hiding from a contagion tied to the destroyed research station on Phoebe.

Before they can leave, Eros declares a radiological emergency. CPM contractors in stolen Ceres gear herd crowds to “shelters” that are death traps—gassing citizens and bathing them in radiation to cultivate the organism. Holden and Miller, irradiated while proving the trap, race for the Rocinante as infected survivors begin to shamble out. They escape with Naomi and Alex, but not before witnessing Eros’ conversion into a live experiment under corporate control. Soon after, they capture a derelict stealth ship chained to Julie’s coordinate and recover logs and a Protogen briefing: the “protomolecule,” an ancient payload meant to repurpose early Earth, has been found at Phoebe and is now being tested at human scale.

Earth and Mars trade blows; Fred Johnson coordinates an OPA strike on Protogen’s Thoth Station, the experiment’s observation hub. The Rocinante disables station defenses, and OPA boarders—Miller among them—take operations and capture Protogen executive Antony Dresden. Dresden coldly argues that Eros was necessary to understand and control the protomolecule, promising engineered humanity if his work continues. Holden seeks a trial; Miller judges that Dresden will talk or buy his way free and summarily executes him, rupturing his ties to the Rocinante.

With Eros still active, Miller proposes an audacious quarantine: wire the docks with fission mines and ram the asteroid into the sun using the Mormon generation ship Nauvoo. Fred backs the plan. The Rocinante deters an approaching UN science vessel; Miller leads teams to plant bombs on Eros and chooses to remain behind as the Nauvoo closes. At the moment of impact, Eros reorients itself and the ramming misses—the protomolecule is flying the rock.

Holden’s ship and a UN corvette give chase as Eros accelerates silently, vanishing from radar while glowing on thermal. Fearing an Earth impact, Fred and UN command ready a massive nuclear strike. Holden can’t keep up without killing his crew; he instead has Naomi reactivate docked freighter transponders on Eros so Earth’s missiles have targets despite the stealth. The salvos launch even as Miller, still on the surface, arms a fusion bomb and hauls it into the station.

Inside, Miller follows a heat gradient through corridors reworked from human remains and realizes Eros is thinking with stolen minds. Julie’s consciousness is the template steering the station—her instincts and goals fused with alien purpose. He asks Holden to buy time; Naomi and Fred spoof the missile targeting across Belt beacons, delaying the strike without losing control. Running out of air, Miller deduces Protogen hid Julie in backup environmental controls. He finds her alive, merged into the lattice, wakes her, and, exposing himself to infection, talks to the person within the monster.

Miller asks Julie to choose another destination. Appealing to her ethics and independence, he persuades her to turn from Earth toward Venus. Eros veers; the UN standoff with the Rocinante dissolves as the catastrophe is averted. In Venus orbit, Eros disassembles into a vast, crystalline bloom that seeds the planet’s atmosphere—evidence of a larger, unfinished program.

In the aftermath, the Rocinante limps back to Tycho. Holden and Naomi choose each other. Fred convenes negotiations on Ceres, balancing the Belt’s future against Earth–Mars suspicion and quietly holding a live sample as leverage. He plans to use Miller’s sacrifice as symbol; Holden argues for honoring the man. Above it all, Venus grows strange towers, and the protomolecule’s design continues—proof that the human arguments are happening in the shadow of something older and patient.