We pan over a lifeless body before settling on Dr. Marin. He doesn't believe the CDC is coming back for them; he wants to force the cooperation of those upstairs by shutting off the "oxygen scrubbers," which they can do from Level R. Level R is bigger and can last longer once the air's cut off. Julia thinks it's a horrible idea; shouldn't they focus on re-establishing communication? "This is communication," Marin grunts, and kicks Jules out of the bunker. In the hall, a mysterious figure in a vintage gas mask beckons to her, but when she follows it around a corner, it disappears.
Hatake sips gloomily from a Keep Calm & Carry On mug -- ironical! -- as Alan fumes about the loss of the satellite and protests leaving those on Level R to die. Hatake explains, as though it's not all his fault in the first place, that they have to contain the contagion. "Just abandon the sick and the dying?" Alan asks incredulously. "Yes," Hatake says. Jeez.
After the perky title card, stupid lying Sarah and her stupid shaking hand freak out some more. A knock on the door startles her into spilling half her Pills Of Significance down the sink; it's a doctor Sarah tested yesterday, who asks if Sarah's sure she didn't get any false negatives, and shows Sarah a lesion on her arm.
Alan meets with Balleseros, who continues to act jumpy and weird without anyone noticing, and Doreen, who's no closer to isolating a Patient Zero. Sarah arrives late and says something in computer-sequence-speak. Next, Alan visits Peter, who's dying, and pushes the doctor on-site to try the universal treatment on Peter, even though it's never been tested on humans.
Elsewhere, Hatake thinks Balleseros is dumb for blowing up the satellite dish; Balleseros has to point out that it's that, or word gets out that Hatake's project has gone pear-shaped. Hatake sniffs that Balleseros is too dumb to understand his results, but Balleseros is smart enough to know that "our employers" want the results Hatake promised, not this "sh*tshow." Then the computers go bazoo: the oxygen scrubbers have shut down, and Balleseros asks, "Is that bad?", so maybe he is kind of dumb.
Aerov explains the CO2 implications of the shutdown. Balleseros wants to get some guns and go "reason with" Level R, but Hatake says he'll handle it. "Like you've handled everything else?" Balleseros snarks. Good point. He stomps off.
The doctor's retest comes back clear, but she doesn't believe Sarah and begs her not to send her to Level R. Sarah tries to reassure her while, in Peter's cubicle, the serum appears to work, at first.
Doreen's fed up with Balleseros's "Fox Mulder crap," so he "admits" that he's with the Pentagon, investigating rumored "gene delivery vehicles" that the virus may be a smokescreen for. Meanwhile, Jules is getting chased out of her hiding spot by a vector -- and yanked to safety by the masked figure just in time. After giving the vector a gnarly compound fracture with a steel door, "Jay." reveals herself, but only after Jules begs her to. Jay is also a multi-degree researcher, and says Hatake hid bunkers all over the place on Level R, just in case.
Alan notes that Peter is "marginally stabilized," then tells his unconscious brother that he basically saved Alan from their alcoholic father, but it's not going so well elsewhere; Sarah's visitor is hallucinating, and oxygen levels keep dropping. Sarah realizes her test doesn't work, at the same time her visitor, an oncologist, realizes Sarah has a tumor (tha'ts what's caused the trembling hand!) and Doreen realizes "someone designed this virus." Can she tell what for, Balleseros asks? Not yet, but she'll find out. Balleseros stares at her, probably thinking he'll have to kill her soon. Sarah's stammering through an admission that her test sucks when Peter wakes up and distracts Alan with a fraternal reunion. Finally she tells him, but denies anyone on their floor is infected. She's shame-spiraling, but Alan gets her refocused on fixing the test and freeing those on Level R as Hatake responds to Aerov's report on everyone's CO2 symptoms -- which sound a lot like the viral symptoms -- by revealing a secret room in his office.
And the secret Peter has to reveal is that he's not entirely sure when he is, talking about their father as though he's still alive. Alan looks wrecked. So do Jules and Jay, who can't find any supplies and have to hide behind a busted cabinet from the vector they fought earlier; and Peter's doctor, who has to inform Alan that Peter's viral load is on the increase again. There's nothing else they can do; Peter doesn't have long.
It doesn't take Peter long to realize he's dying. He bitches that Hatake recruited him under false pretenses, assigning him scut necropsies and only taking an interest in his connection to Julia. Then the brothers apologize to each other some more, but Peter admits he didn't get with Julia only once; it happened whenever Alan went to a conference. They couldn't stay away from each other, so Peter went to the Arctic. Then Peter flatlines before Alan can kick his ass.
The shaking in Sarah's hand is much worse, and she nearly faints in Hatake's office, then ransacks the supply closet while Peter's doctor updates his chart. Peter's still alive, barely. As Sarah doses first her visitor, then herself with morphine, Jules and Jay discover a store of food rations -- and something much more disturbing, namely Jules's initials and favorite flower carved into the closet wall, in her child self's handwriting. "I've been here before," she quavers. Brr!
Hatake's visit to Level R goes well...for him. He Jedis Marin and the gang into agreeing that they all have to work together to live; Marin turns the oxygen back on; Hatake grabs Aerov's pistol and shoots everyone except Aerov, who looks nauseated. Hatake spins it as him protecting Aerov, then orders him back upstairs. He has something to take care of, which he doesn't specify, but Aerov and the rest of us know it's about Jules.
Doreen has found an unidentified protein, one never seen before; it's going to manifest some trait the DNA's designer wants humans to have, but she doesn't know what, or why, just that it's made from animal and human material spliced together. Balleseros looks regretful about what he's about to do, which is stab Doreen in the neck with a needle.
Hatake meets the vector in the hall, stares him down, and passes unharmed. Balleseros dumps a shelving unit of naked rats onto Doreen's dying body. Yikes!