Season five begins with the solar system in a fragile state. The Ring Gates, leading to thousands of new worlds, are now controlled by the Earth-Mars Coalition. A power vacuum has emerged, with the Outer Planets Alliance splintering into factions. The crew of the Rocinante, having helped open the gates, are now taking a much-needed break, scattered across the system.
James Holden remains on Tycho Station, trying to convince the OPA’s leader, Fred Johnson, to secure the last remaining sample of the protomolecule. Meanwhile, Amos Burton travels to a troubled Earth to settle the estate of a woman who was like a mother to him in Baltimore. He finds a planet struggling with the new economic reality post-gates, and he becomes embroiled in the underground chaos.
On Mars, Alex Kamal reunites with his old friend Bobbie Draper, now a disillusioned former marine. Together, they uncover a shocking conspiracy: elements within the Martian military and government, seeing no future for Mars as people flock to new planets, are secretly selling advanced warships and technology to Belter factions.
The heart of the season, however, belongs to Naomi Nagata. She receives a distress call from her estranged son, Filip, and is drawn back into the orbit of her former partner, the radical Belter terrorist Marco Inaros. Marco has been quietly consolidating power, and he unveils a devastating act of war. Using stealth-coated asteroids, he launches a coordinated attack on Earth, with one asteroid striking the Atlantic Ocean and causing a colossal tsunami that devastates the planet.
As Earth reels from the catastrophic impact, Marco declares Belter independence, framing the attack as a righteous strike against the oppressors of the Inners. Naomi, trapped on Marco’s flagship, realizes his plan includes using the protomolecule sample he has stolen to further his reign of terror. She is forced into a desperate and painful game of sabotage and psychological warfare against her own son and his father.
Holden, with the help of the journalist Monica Stuart, races to expose Marco’s connection to the asteroids and the stolen warships. On Earth, Amos fights his way through a collapsing Baltimore with the help of an old friend, eventually securing passage off-world. Alex and Bobbie, in a stolen Martian gunship, chase down one of Marco’s allies to gather proof of the conspiracy.
The season builds to a tense climax. Naomi manages to send a warning, but at great personal cost, nearly sacrificing herself to escape. The Rocinante crew reunites in space, responding to a distress call from a ship under attack. They arrive to find the ship destroyed and Filip’s vessel, the Pella, fleeing. In a moment of vengeance, Alex pursues the ship at high speed, but the strain causes him to suffer a sudden stroke, killing him alone on the pilot’s deck.
The season ends with a system at war. Earth is crippled, its government in disarray. Mars is collapsing from within due to the betrayal. Marco Inaros stands triumphant, commanding a formidable fleet and holding the protomolecule, his vision of Belter supremacy seeming within reach. The Rocinante crew is left fractured, mourning the loss of Alex, and facing a seemingly unstoppable enemy who has changed the balance of power in the solar system forever.