Two hundred years in the future, in a fully colonized solar system, police detective Josephus Miller (Thomas Jane), who was born in the asteroid belt, is given the assignment to find a missing young woman; Julie Mao (Florence Faivre). Meanwhile, James Holden (Steven Strait), the first officer of an ice freighter, is witness to an unprovoked attack upon the ship, by craft believed to be from Mars (MCRN Federation). As news of the attack spreads throughout the system, the incident's flow-on threatens to destabilize already tenuous relations between Earth, Mars and The Belt. Far away from the struggles in deep space, on Earth, Chrisjen Avasarala (Shohreh Aghdashloo), a powerful United Nations executive and diplomat, works to prevent war between Earth and Mars by any means. Soon, the 3 find out the missing woman and the ice freighter's fate are part of a vast covert conspiracy which threatens all humanity. Written by nano_tech

Unlikely allies Joe Miller and the crew of the Rocinante led by Jim Holden uncover more about the conspiracy to release the proto-molecule on Eros station.

Holden and crew stage a dangerous raid in search of information about the protomolecule.

Holden and Miller butt heads about how the raid was handled.

Miller devises a dangerous plan to eradicate what's left of the protomolecule on Eros.

The protomolecule-infested asteroid Eros has dodged the commandeered Nauvoo's collision course, and begins propelling itself toward Earth with Miller aboard and the Rocinante in pursuit. Guided by the Rocinante's sensor scans, Miller takes his dead-man's-switch nuclear bomb into the asteroid to destroy the 'seed crystal' believed to be controlling the protomolecule's activities. Meanwhile Earth's government debates whether Eros has been weaponized by Mars, and launches a volley of nuclear missiles to intercept it. The asteroid unexpectedly deploys stealth technology and accelerates, causing the inbound missiles to lose their target lock. Holden has Fred Johnson relay an offer to Earth, to use the Rocinante's sensors to 'paint' the asteroid so that Johnson's technicians on Tycho station can guide the missiles. Earth's military suspects Johnson of trying to hijack control of the arsenal, but following a plea from Holden, Avasarala vouches for him. As the Roci enacts their plan, Eros ... Written by nomen_meltdown

The UN organizes a science expedition to the Eros crash site on Venus. The crew of the Roci discovers that 30 of the nukes launched by Earth are missing. Violence erupts on orbit around Ganymede. Bobby and the MCRN marines face a new threat.

The mystery of the cause of the Altercation between UN troops and Mars Marines at the farming colony is still unknown but a discovery of a seventh man leads to a cover up by the Martians so as to avoid an all out war with Earth. Meanwhile Fred Johnson has an important asset stolen from him by an old friend and Naomi is dealing with guilt for lying to Holden about destroying the Proto Moloecule sample that was hidden. Written by Bobby Ssendagala

Naomi tracks down signs of protomolecule and Fred Johnson's control over OPA collapses.

Bobbie becomes a pawn in a struggle between Earth and Mars.

Holden leads his crew through the war-torn station on Ganymede.

Bobbie makes a decision that changes her life forever.

A discovery pushes Naomi and Holden apart and sets the Roci crew against each other.

In the final episode of this season, the crew of the Rocinante comes face to face with an evolving intelligence infused with the alien protomatter.