The crew of the Roci investigates a strange protomolecule ruin on an alien planet. Bobbie copes with civilian life on Mars. Drummer and Ashford battle with piracy in the Belt.

Avasarala is blindsided while on a visit to Mars. The Roci crew continue their protomolecule investigation while tensions between the RCE and Belters reach a tipping point. Drummer and Ashford track down a terrorist.

New alien threats emerge on Ilus as Naomi battles health challenges on the planet. Bobbie searches for a missing person on Mars. Avasarala faces a new challenge in the UN.

Drummer and Ashford confront a dangerous person from Naomi's past. Murtry hunts down a target. Bobbie's makes a life-changing confession.

As tensions on Ilus reach a boiling point, Holden reveals a secret. Avasarala debates Nancy Gao while an emergency on the Roci forces Alex and Naomi into action.

The Roci crew prepares for an incoming disaster on Ilus. Ashford and Drummer close in on an enemy within the Belt. Bobbie takes on a dangerous job.

Naomi and Alex work to keep the Barbapiccola in orbit amidst a power outage. Avasarala faces a tough decision. Holden and Elvi race to find a cure for a disease spreading on Ilus.

Avasarala faces fallout for the UN's military mission. Ashford and Drummer makes big decisions about their future within the OPA. A spreading illness on Ilus takes a toll on Amos. Alex and Naomi's attempt to rescue the Barb turns desperate.

Holden and Miller race to save Ilus. Murtry puts his endgame into motion, putting the Roci crew's lives at risk.

Ashford closes in on an enemy while uncovering a dangerous plot. Avasarala faces a crossroads in her personal and political life. The Roci crew works to reestablish life on Ilus in the wake of a deadly catastrophe.