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.

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.