The final season opens with the Solar System on the brink of total war. The fragile peace between Earth, Mars, and the Belt has been shattered by the actions of Marco Inaros and his Free Navy, who now control the ring gates and the resources beyond them. Earth is reeling from the catastrophic asteroid attacks, its atmosphere choked with debris, leading to widespread famine and death. Mars, its dream of colonization faded, sees many of its best warships and soldiers defecting to Marco’s cause.
The focus tightens on the crew of the Rocinante. Holden, Naomi, Amos, and Clarissa “Peaches” Mao are now officially working for the Transport Union, led by Camina Drummer, in a desperate alliance to combat the Free Navy. Their mission is to disrupt Marco’s supply lines and rally what remains of the Belt’s factions against him. Drummer and her small fleet, loyal to the memory of Fred Johnson, walk a razor’s edge, publicly pretending to align with Marco while secretly aiding the Rocinante.
A central emotional thread is Naomi’s struggle. She works tirelessly to find a way to reach her son, Filip, who remains under Marco’s manipulative control. Using her unparalleled skills as a Belter engineer, she devises a dangerous plan to send a message across the void, hoping to show Filip the truth of his father’s monstrous ego and the dead-end future he offers the Belt.
Meanwhile, a new and even more terrifying threat emerges from the ring space. Unknown entities, which the crew dubs the “Strange Dogs,” are altering matter and biology on the abandoned colony planet of Laconia. This storyline follows the young daughter of the renegade Martian commander, who witnesses these bizarre, seemingly magical repairs that come at a horrific cost. It’s a chilling glimpse of the alien technology that humanity does not understand and cannot control.
The climax builds toward a massive naval battle near the ring gate. Marco, overconfident and seeking a decisive victory, is outmaneuvered by the combined strategy of the Rocinante, Drummer’s rebel Belters, and what remains of Earth and Mars’ fleets. The battle is a brutal and costly victory for the allied forces. In a final, pivotal moment, Naomi’s message reaches Filip. He sees the recording of his father callously admitting he used Belters as pawns and would gladly sacrifice his own son for his legacy. Disillusioned, Filip secretly abandons Marco’s ship.
Defeated and alone, Marco Inaros makes a desperate, last-ditch run through the ring gate, pursued by the Rocinante. He hopes to rally his forces on the other side, but instead finds his allies have abandoned him. With no other options, he chooses to go out on his own terms, committing suicide by decompression as Holden watches. The immediate war is over.
In the aftermath, a fragile new order begins to form. The Transport Union solidifies its control over the ring gates, with Drummer as its President, striving for a future where the Belt has a true seat at the table. On Earth, the long, slow process of ecological recovery begins. The Rocinante crew, weary but together, decides to take on a new, quieter role as an independent security contractor for the Transport Union.
The season ends with a poignant coda on Laconia. The little girl, now fully transformed by the Strange Dogs into something new and alien, presents herself to her father, the commanding Admiral. As a massive, organic-looking warship, built by the same unknown technology, rises from the planet’s ocean, it’s clear that the defeat of Marco Inaros was merely the end of a chapter. A much larger, more alien story for humanity is just beginning.