Ignoring Prax's pleas to let him communicate with the creature, Holden, Amos, and Alex go after the hybrid, after it removes an implant from its chest and throws it out of the ship. It throws a magnetic crate at the men, and it pins Holden to the wall. Alex and Amos are forced to retreat, as the bullets in the hybrid heal themselves.
Strangely, the hybrid ignores the trapped Holden and starts digging into the ship's bulkhead. They realize it's going after the ship's radiation source, for food. If it reaches the ship's reactor, they're all dead.
Back at the shootout on Mao's ship, Avasarala, Cotyar, and Bobbie are in trouble, though they've reached a stalemate. They spot an air vent, and Cotyar tells Bobbie to escape through the elevator shaft, retrieve her battle armor, and come back to save them.
As the hybrid continues to dig, the Roci crew needs to figure out a plan before Holden's injuries become life-threatening. Amos speaks up with a plan to depressurize the cargo bay and shoot the hybrid out into space. But won't that plan tear Holden apart? "Maybe not," says Amos.
On the Roci, Naomi gets Amos alone and apologizes for getting rough with him on the Somnabulist. He's angry at himself for making her. He says he's been making all the wrong choices. Naomi intuits that Amos was lying when he said Holden could survive the de-pressurization plan. She tells him he's not to blow the doors on that hatch until she finds another way.
With the hybrid still digging, Alex turns off the ship's reactor. But once the hybrid can't sense the radiation anymore, it turns its attentions to Holden and begins advancing on him. Bad news. So Alex powers up again, and the creature resumes digging.
Holden's vital signs are fading, and Naomi hasn't been able to figure out an alternative to Amos' plan. So Holden wants to have a talk. Naomi refuses to let him say goodbye, but he presses on. He tells her that if he dies, let him go and find a place to hide out.
Cotyar is passed out from his wound, until Avasarala presses on it to wake him up. They're still trapped, but Mao's men offer Cotyar a deal: give up Avasarala and he can walk. To Avasarala's shock, he's considering it. Why should they die for their boss' conflicts, Mao's guy asks. Avasarala tells Cotyar that if he is going to turn on her, he must take up her cause. Someone has to stop Errinwright.
Prax gets an idea: the hybrid is moving towards the energy source like a plant to sunlight. If they could offer it a new energy source, they could lure it outside the ship with a nuke and then blow it up.
Meanwhile, the only thing standing between Bobbie and her supplies is a dweeby electrician. He threatens to push a button and initiate a lockdown, but she calls his bluff. They strike up the same bargain being offered to Cotyar: why should they sacrifice themselves for Mao and Errinwright? Or Earth and Mars, for that matter? The electrician lets Bobbie pass, though he asks that she rough him up to make a good show of it.
As Prax and Naomi walk the outside of the Roci, preparing to toss the nuke, Holden makes Amos promise to blow the hatch in case the plan doesn't work. "You were always trying to be a good man," Amos tells Holden. "Not everybody does. Thank you."
Alex shuts off the power source again, but this time as the hybrid moves towards Holden, Prax and Naomi expose the core of the warhead. The hybrid senses it and follows it outside the ship. It looks for a second like Prax will lose his nerve, but he doesn't. He tosses the warhead, he and Naomi run, and Alex is able to roast the hybrid and the nuke with the Roci's afterburners.
The Arboghast descends to the surface of Venus and the Eros crater when suddenly, the sensors go crazy. The crater is moving! The Martian ship completely disappears, and we soon see why, as the Arboghast is surrounded by Protomolecules and then suddenly pulled apart.
Safe on the Roci, Naomi tends to Holden. She tells him they can't have any more secrets between them, so she tells him the truth about the piece of Protomolecule she said she shot into the sun. Only she didn't. She tells Holden that there's no going back: the Protomolecule is a weapon they'll all have to deal with. Earth has it; Mars has it; she needed to make sure the Belt had it. So she gave the Protomolecule to Fred Johnson.