Sarah walks the halls on her own, and is set upon by a vector who pops out of a heating vent. That carelessness is deliberate: Sarah's bait to catch a vector for testing. Hatake wants him back upstairs, but Alan notes that, since the other vectors took his brother, "Level R seems almost abandoned" -- where did the others go? If Hatake knows, he's not saying. He's also not admitting that there's yet another level below Level R. Aerov grunts, "Tell them everything, or I will." After an ice age (as it were), Hatake sighs, "Level X." Aerov adds disgustedly that it's where the virus vault is. Oh, and by the way, they have original core samples of Narviks A and B down there.
You can imagine how happy Alan is to hear that 1) they've had samples all along that 2) Hatake created, i.e. he's furious. Hatake claims that he used his mandate from Ilaria to make "something more beneficial." Alan isn't having it, but Hatake warns them all that Sutton -- whom he dismisses mysteriously as no longer "a problem" -- is just a messenger; an army is coming. Alan's like, fine, let's destroy the virus before Ilaria gets to it, as if it's that simple.
Meanwhile, Jules demands an explanation from Hatake, who allows, "We have... met before." Well, duh. Jules's mother was a top cell biologist, and Hatake's mentor; he visited her in Montana several times. Jules points out that he looks exactly the same in a 30-year-old picture. He shrugs that he was very young, and keeps claiming it's a coincidence that Jules is at the base now.
After Alan determines from Dr. Adrian's experiment that extreme cold is the only way to neutralize vectors en masse, Balleseros's new cellmate, the ginger stormtrooper, tries the doors while mentioning that Ilaria is coming in "full force" in two days -- can't Balleseros get them out of there? Balleseros is no match for an electromagnetic seal. The stormtrooper, Klein, and Balleseros freak out that Ilaria will bomb the base not knowing they're still inside. Balleseros freaks out more when Klein lets it slip that Sutton sent men to Anana's village to burn it, and her, to the ground.
The vectors show up in camera footage from Level X; they've gathered near a heat source. Aerov explains that Level X is the remains of a Russian trading post from the 1850s. Hatake says there's a secure staircase and offers to go down, but Alan doesn't trust him, though he doesn't know how he'll get past the vectors himself. Sarah calls their attention to the vectors' swarm behavior, and out of sight of the cams, they've gathered around Peter and to spit black blood into a Keep Calm And Carry On mug. It's nice that they can work together towards a common goal; it's also revolting. The blood is tipped into Peter's mouth, and he awakens, then springs up onto a shelving unit and induces the other vectors to kneel before him with a hand gesture, so apparently he's their leader now.
Alan briefs the team on the strike plan. Jules wants to go alone because vectors don't attack her, but Alan says no; they don't know why vectors prey on some but not others. As Sarah battles a hand tremor from her brain tumor, Hatake gives Alan a gun. Alan starts to hand it to Jules but Hatake interrupts: "She won't need it. You will." Alan reviews the operation: Sarah and Hatake turn off all the systems in sequence as Jules and Alan descend to Level X. Aerov will hand out thermal blankets to survivors while the dropping temperature knocks out the vectors. We see this happen in a montage, and after the base is left in darkness, Sarah almost drunkenly tells Hatake that she'll die soon and leave nothing of consequence.
Alan and Jules head down. Balleseros sees an opportunity to break out. Alan says that, if the plan fails, they'll have to burn the base down. "How will we get home?" Jules asks. "We won't," Alan says after a long pause. They emerge at the bottom of the secret stairs amid a crowd of frozen and becalmed vectors. In the vault, Jules gapes at the racks upon racks of containers: "There are too many." The base has more strains of some viruses than the CDC does, and Jules wants to destroy everything to screw Ilaria. Alan protests that there isn't time, then assents.
Balleseros and Klein escape, but Klein doesn't get far before Balleseros beats him with an iron bar to get his coat. Elsewhere, Sarah is babbling about seeing death, and Hatake is forced to turn the power back on himself when she has a seizure at the critical moment. Downstairs, Alan and Jules find the Narvik strains are missing; they've run out of time. The vectors are waking up.
Aerov hurls Balleseros off the snowmobile he's trying to steal, only to hear that Sutton sent stormtroopers to kill Aerov's siblings. Asked why he cares, Balleseros groans that at some point "it just has to stop." The two men team up.
Alan has to fight his way through the vectors, but Jules can stare them down and pass unmolested. They're almost clear when Jules sees another set of her childhood initials, and a ladder going down into a vent. She insists she's there for a reason -- again; her mother must have brought her to the base as a kid. She's not asking him to go, but of course he's on board. Down below, Jules looks nauseated to see a replica of her childhood home in Montana, and Aerov is just as disturbed that he's lost the trail. Fortunately, Anana finds them, and the group heads to the village hoping to beat the Ilarians that passed by earlier.
Jules struggles to remember something about her mother as Alan wonders why Hatake would build an exact copy of her summer home. Jules remembers Hallucipeter telling her, "It's always been about you," and Alan snarks that maybe it's her subconscious talking. They start to leave while Aerov, Balleseros, and Anana watch the Ilarians loading villagers into a trailer. They're outnumbered, but Balleseros pretends he's captured Anana to get them closer; Aerov maintains the story by punching his twin, Tulok. He also glares a lot.
Sarah thinks Hatake is Alan, and whispers that she's sorry she didn't tell Alan about the tumor. Hatake finds the scar from a failed surgery on Sarah's neck. Alan and Jules come up and are quickly surrounded by Peter and his vector groupies. Jules keeps them away with her silver death stare, and as she and Alan escape, Peter roars in frustration. Alan wants to know how Jules knew what to do. She's not sure.
Tulok also makes a narrow escape when Balleseros, Aerov, and Anana manage to shoot the Ilarians before they can execute Tulok and the others; Tulok thanks Aerov by punching him in the face.
The elevator opens on Hatake and Sarah, on the ground. Hatake snaps that Alan should have known about Sarah's tumor. Alan bundles Sarah off to the ICU, but not before basically accusing Hatake of lying about the virus, though Hatake looks genuinely horrified that the Narvik wasn't there. Alan blames himself for not seeing the signs of Sarah's illness, and Jules helps him tend to Sarah until Sarah feverishly mutters that she and Alan Did It, and Jules is awkward and leaves... ...to ask Hatake again what the H she's doing there. His answer is to show her the half of the photo with her mother in it -- and her mother is Jaye (Julia's hallucination from a few episodes ago), or what "Jane" would have sounded like to a four-year-old. He non-answers that the replica of the cabin isn't a replica, then takes out his contacts to show her his silver irises -- and tell her what we figured out weeks ago: "You have your father's eyes." Jules backs away in horror.
Aerov and Tulok reminisce about Matchbox cars; Anana patches Balleseros's gut wound; Alan strokes Sarah's head; Jules looks at the photo and cries; Hatake also cries after Jules flees; and Dr. Adrian swigs vodka and packs a bag, including the Narvik strains. Uh-oh.