The episode begins with a flashback. Shane is at the hospital, visiting the still comatose Rick, when the halls are overrun by military in gasmasks and other protective gear. Shane watches as the soldiers shoot down innocent civilians. He tries to escape with Rick, but worries that the machine is the only thing keeping Rick alive. The power suddenly goes out, and the machine shuts off. Shane checks Rick's chest for a heartbeat but doesn't hear one. Upset that he needs to abandon his best friend, Shane leaves Rick's hospital room, shutting the door and blocking it with a gurney.
Continuing on from last week, Dr. Jenner allows the group inside the walls of the CDC, but he warns them that once the doors are shut, they can't be opened again. Everyone must submit to a blood test before they are fully welcomed inside. No one turns out to be infected, so Jenner gives them full access to the facility.
The group enjoy hot showers and meals with wine. Jenner explains that he's the only staffer left after everyone else either went home to be with their families or killed themselves. Later Lori is alone in one of the facility's rec rooms, but a drunk Shane finds her and tries to force himself on her, explaining that he was sure that Rick had died. She reminds him that Rick isn't dead and that they can't continue on the way they were, but Shane isn't listening. Lori finally has to shove Shane off her.
The next morning, Jenner shows the group footage of a test subject (number 19) who was infected and agreed to be observed. The subject's brain activity dies, but then the infection causes the brain stem to reactivate. However, everything the person was (personality and memories, the higher functions of the brain) is gone. Test subject 19 was eventually shot in the head. The group realizes that the test subject was actually Jenner's wife, and he eventually had to kill her.
Dale notices a countdown clock and asks Jenner for details. Jenner admits that the facility is under lockdown and will undergo decontamination, which will wipe out all life in the facility (including all the deadly contagions the CDC had kept samples of) and destroy the building. The group pleads to leave, but Jenner reminds them that he can't open the doors.
The group also discovers that power to the facility is running out, so even if they stop the countdown, survival is still next to impossible. Jenner insists that this is the best thing for everyone, since nothing is out there anymore. Rick counters by saying that there has to be hope. Jenner agrees to open the doors one final time. Before Rick leaves, however, Jenner whispers something in his ear, which disturbs Rick.
Jacqui and Andrea decide to stay, thinking that they don't have anything left to live for, but Dale manages to convince Andrea that Amy would not have wanted her to die like this. Rick uses a grenade to shatter the glass at the front entrance and allow a means of escape, and Dale and Andrea rush out of the facility just as the bomb detonates.
The CDC building is destroyed and the survivors drive away, destination unknown.