WARNING: The following contains major spoilers for The Expanse Season 5, Episode 7, "Oyedeng," available now on Amazon Prime Video.
The Free Navy seemingly sprouted up out of nowhere on The Expanse, somehow gaining followers and ships along the way. As Bobbie discovered in Season 4, Mars was selling technology to Belters, which resulted in Marco Inaros' bombardment of Earth with stealth composite-coated asteroids. However, the Free Navy also managed to get its hands on Martian warships without paying for them. Now, Season 5, Episode 7, "Oyedeng," has revealed that Mars' price for selling warships to the Free Navy was the final protomolecule sample and the services of Dr. Paolo Cortázar, a researcher who studied the protomolecule and was last seen in Season 2.
It's Monica Stuart who figures out what Mars is up to. She reasons the Free Navy couldn't possibly afford its numerous Martian warships unless it had something that was worth more -- and that something would be the protomolecule sample recently taken by the Zmeya. In her discussion with Holden in the Rocinante mess hall, Monica suggests Cortázar must be part of the deal, stating "he's useless without a sample and it can't be coincidence that they were both just taken."
Holden and his makeshift crew are searching for the Zmeya, during which Alex contacts him, alerting him to the scale of the Free Navy and sending profiles for the many ships flying its flag. The ship profiles and drive signatures allow Holden to locate the Zmeya. At the same time, however, he notices that Naomi's ship, the Chetzemoka, is also on the list. Sticking to his current mission, he tasks Alex with keeping tabs on Naomi's ship.
With Alex tracking the Chetzemoka, Holden and the Rocinante go after the Zmeya, entering a dogfight with the Free Navy ship upon finding it. Bull, the Roci's temporary pilot, puts the ship into a spin as its point defense cannons take out all the missiles the Zmeya shoots at them. Holden then fires up the Rocinante's famous keel-mounted railgun and clips the Zmeya's drive cone, leaving the ship on the float. Holden sends the Zmeya's crew a message instructing them to power down and prepare to be boarded, but instead they opt to overload the Zmeya's reactor and sacrifice themselves.
The Zmeya's explosion is significant because it must mean the protomolecule sample was moved to another ship. With Monica and Holden's realization that the sample must have been used as a bargaining chip with Mars, its unlikely this will be the sudden end of all things protomolecule. Cortázar's mention also indicates his return at some point in the future is almost certain.
Furthermore, the revelation of Mars' deal to acquire the protomolecule sample and Cortázar means the planet has traitors. The Free Navy's attack on Earth was coordinated with an attempt on the Martian Prime Minister's life, so whoever is in league with the Free Navy is evidently separate from Mars' government. What they intend to do with the protomolecule is unknown, but its clear whoever holds the sample will be a force to be reckoned with.
An adaptation of the novel series of the same name by James S.A. Corey, The Expanse stars Steven Strait, Cas Anvar, Dominique Tipper, Wes Chatham, Shohreh Aghdashloo and Frankie Adams. New episodes of Season 5 premiere Wednesdays on Amazon Prime Video.