S2E13 · Caliban's War

Complete story — includes the ending

The protomolecule monster is found in the cargo bay on the Rocinante. It attacks Holden, crushing his leg and pinning him to the wall. It tears out panels to get to the reactor core for its radiation. Amos says the only way to get rid of it is to use the air on the ship as a pressurized blast to force it into space, which would also kill Holden. Prax sees the monster craves radiation and suggests the nuclear core in a ship's missile could lure it out. Naomi and Prax expose a core; Prax throws it into space. The monster jumps after it and is incinerated by the main engine. Cotyar is wounded in a shootout with Mao's men. Bobbie manages to sneak away to get her power armor and saves him and Avasarala. As the science team on the Arboghast begins a descent to the surface of Venus to examine the protomolecule structure, the ship is stopped and disassembled in an increasing spherical pattern. Naomi confesses to Holden that she never destroyed their protomolecule sample; with Earth and Mars already fighting over it, the Belt needed it too, so she gave it to Fred Johnson. On Io, Mei and other children are shown to be kept in stasis by Dr. Strickland.