The Vest Guy from the last episode is unhappy being in isolation. He starts day 4 by telling Julia about his plan to get out by cutting off the air supply to the whole base. The people upstairs will be affected more strongly because they have more people and less empty space. Julia suggests it's more important to get the communications back up so Vest Guy kicks her out. In the hallway Julia sees someone in a gas mask motioning for her to follow. She does but when she turns the corner the masked figure has disappeared.
Back upstairs Alan makes the case to reopen the isolation area since Balleseros blew up the comm link, but Hataki refuses while sipping from a mug that displays his appreciation for either classic motivational posters or overplayed Internet memes.
Sarah is trying to take her medication with a shaky hand when she hears a knock at the door. It is a woman who got a negative result from the test but has symptoms of the infection. Sarah doesn't believe that the test is flawed and doesn't mention it to Alan when the team meets up.
At the meeting Alan says the only contact with the outside world is periodical supply drops. After the meeting Alan goes to treat Peter. He wants to give him the uber-drug against the wishes of another doctor.
Balleseros goes to Hataki and encourages him to deliver the results he promised their mysterious employers. Just as Hataki raises a finger to suggest his disapproval the alarm goes off. Vest Guy has shut off the oxygen supply and carbon dioxide levels are rising. Daniel says they have 6 hours at the most to get the Oxygen back and 2 hours before people start experiencing symptoms. Hataki says that he and Daniel will go to negotiate alone. Meanwhile, Balleseros admits to Doreen that he isn't what he wants people to think, and that he's overheard rumors that the virus is meant to be a DNA delivery system. Doreen later confirms it, and says that the virus was designed to force people to develop a certain trait.
Rejected by her fellow invalids, Julia sits alone when she sees a vector going through a supply closet. She is saved from the vector by the person in the gas mask. She reluctantly takes off the mask and tells Julia that her name is Jaye, she has several degrees, and she knows where to find food.
Peter is responding positively but slowly to the uber-drug. Alan gives him a pep talk, thanking him for helping him survive their abusive father but says that Peter owes him for the night he found him in bed with his then wife, Julia.
In Sarah's bedroom the infected woman starts to hallucinate, causing Sarah to admit that her test is not accurate. Then the woman reveals that Sarah has a tumor. When Sarah goes to tell Alan about the test, Peter interrupts, showing signs of recovery and consciousness. When Sarah does tell Alan about the test, she leaves out the part about the infected woman in her bedroom.
After Sarah leaves Peter begins talking to Alan as if they were still children. Alan reminds him that their father has been dead for a long time. The other doctor who was against using the uber-drug tells Alan that the virus is returning. When Alan goes back in to talk to Peter, he recognizes the tone from when their mother was sick. Then Peter tells him that he doesn't know what is going on, and that Hataki only wanted him to get to Julia. He also says that his affair with Julia was more than one night. Immediately after that he flatlines and Alan keeps him alive, but in a vegetative state.
After Sarah's tumor causes her to nearly collapse she frantically searches for medication in the storeroom. She finds morphine and gives it to the infected woman before injecting herself.
Sarah and Jaye have found a food supply, as well as a new plot twist. They find Julia's initials on the wall in her handwriting, suggesting she has been to the base before although she has no memory of it. Also, her middle name is Lynn.
Downstairs, Hataki and Daniel tries to reason with Vest Guy and his two henchmen. Hataki gives his word that they can all work together so Vest Guy puts his ax down and turns the Oxygen back on. As Daniel begins to walk away, Hataki takes his gun and kills the three men. He tells Daniel to dispose of the bodies while he goes to find Julia. As he looks for he walks right past a vector and it simply stares at him
Doreen tells Balleseros that the genetic message in the virus is a single strand spliced from animal and human DNA. Then Balleseros tells her that he likes her, then he kills her and drops a shelf of infected rats on her.
Only time will tell how Doreen's death will affect the established formula of she and Balleseros bantering before he goes off and does something shady. Will he find someone new to banter with or spend the entire series being shady?