At the outset of the walker outbreak, Shane visits Rick in the hospital. Army personnel are evacuating hospital staff and executing the infected. Shane tries to lift his comatose partner, but hesitates because of all the tubes and wires attached to Rick.
The power goes out and Rick's monitors die. Fearing the worst, Shane puts his ear to Rick's chest.
Shane reluctantly leaves Rick in the room, barricades the door with a hospital bed and flees the chaos.
In the present, Rick and the other survivors file into the CDC lobby. Dr. Jenner meets them at the door.
Jenner agrees to allow them in - provided they all submit to a blood test. Rick agrees, and they follow Jenner to the building's basement control center.
Looking around, Rick questions the absence of other doctors. "I'm all that's left," Jenner replies.
Later, the group feasts in the CDC cafeteria, jovially drinking wine and liquor, jubilant about finding a safe place. Rick toasts Jenner, who quietly raises his glass.
"When are you gonna tell us what the hell happened here?" Shane asks. Jenner explains that most of the doctors fled. The rest, he says, "couldn't face walking out the door. They opted out." Jenner says that he stayed because he hoped to do some good.
Jenner shows the group around the building, directing the children toward the rec room and imploring everyone not to waste electricity.
The survivors luxuriate in hot showers - all except for Shane, who angrily swallows from a bottle of liquor while he bathes; and Andrea, who sits numbly under the stream.
Afterward, Dale overhears Andrea throwing up. "Everything's gone," she cries. Dale argues they have an opportunity to make a fresh start. "Didn't you see the look on Jenner's face?" Andrea says. "There's nothing left."
Rick stumbles drunkenly into the control room, where Jenner is working. Rick thanks Jenner again. He admits to Jenner that he never let on to the others what he really thought, but he knew they were running out of options. "We'd have died out there," Rick explains. "It'll all be OK," Jenner assures.
Lori finds Carl, Carol and Sophia lounging in the rec room. Carol takes the children to bed while Lori stays behind to browse the library.
Shane looms in the doorway, whiskey in hand, watching. "I'm going to tell you a few things, and you're gonna listen," he says, closing the door.
Lori tries to push past Shane. "How can you treat me like this?" he asks, insisting that he didn't lie to her about Rick. He really thought Rick was dead, that he hadn't heard a heartbeat when he listened for one at the hospital "and I had y'all to think about."
Drunk and desperate, Shane tries to kiss Lori. He grabs for her, forcing himself on her until Lori scratches his face and throat. Horrified by his own behavior, Shane flees.
Rick stumbles into bed with Lori and sees that she's been crying. "We don't have to be afraid any more," he assures her.
The next morning, Rick shuffles into the cafeteria. Shane follows, claiming he scratched his neck in his sleep. "Never seen you do that before," Rick says. "Not like me at all," Shane agrees, eyeing Lori.
When Jenner arrives, he leads the group to the control center, where he displays brain scans from "Test Subject 19," who was infected and allowed the process to be recorded.
The display shows the virus attacking the brain, which goes dark. Jenner fast-forwards to the "second event" - TS-19's resurrection. "It restarts the brain?" Lori asks. "Just the brainstem," Jenner corrects. "The human part, that doesn't come back."
Jenner admits he doesn't know what the disease is or how to treat it, and that he's lost contact with other facilities.
Dale interrupts the stunned silence to ask Jenner about a clock on the far wall, which is counting down from an hour. At zero, Jenner says, "the basement generators, they run out of fuel."
Rick, Shane, T-Dog and Glenn head to inspect the generators. Upstairs, the building's air cuts off.
In his office, Jenner stares at a photograph of a woman, asking her to understand that he did the best he could and hopes she'd be proud of him.
The panicked survivors confront Jenner, who explains the building is shutting itself down.
"It was the French," Jenner says. They stuck it out the longest before they too ran out of power. The survivors try to flee, but Jenner locks them inside the control center.
There's no point in struggling, Jenner explains. Everything topside is automatically locked down. When the building runs out of power, he continues, it will self-destruct - a "decontamination" protocol to keep dangerous infectious diseases from escaping.
Jenner tries to convince Rick to accept his fate. "Last night you said, you knew it was just a matter of time before everybody you loved was dead," Jenner argues.
Rick demands to know why Jenner stayed if he didn't think there was any hope. "I made a promise," Jenner says, to his wife - Test Subject 19 - to keep going as long as he could. She was one of the finest scientists in the world, if anyone could have done something about this, it was her. "Me?" he admits, "I'm just Edwin Jenner."
Lori tells Jenner they just want their chance to keep going as long as they can. Swayed, Jenner agrees to open the door, but maintains they still won't be able to get past the lockdown upstairs.
"I'm grateful," Rick says. "The day will come when you won't be," Jenner counters. He shakes Rick's hand and pulls him close. Jenner whispers into Rick's ear.
The group heads for the exit, but Jacqui stays behind. "I'm not ending up like Jim and Amy," she tells T-Dog, tearfully telling them to leave while they can. "I'm staying too," Andrea says, sliding to the floor.
Dale pleads with Andrea to leave, but she won't budge.
In the CDC lobby, the group finds the doors locked and pounds helplessly on the windows. Carol fumbles in her purse: "Your first morning at camp," she tells Rick. "When I washed your uniform? I found this in your pocket." She pulls the hand grenade that Rick found in the tank from her bag.
Rick detonates the grenade, blasting out one of the glass windows.
In the basement, a resigned Dale sits in front of Andrea. "If you're staying, I stay too," he tells her. She's furious, but he continues, "You don't get to do that. Come into somebody's life, make them care and then just check out."
The survivors run to the cars. From inside the RV, Lori sees Dale and Andrea emerge from the building.
Jenner and Jacqui hold hands and watch the others evacuate on the security monitor.
The CDC erupts in a fiery explosion. Dale and Andrea rush to the RV. Shaken, Rick starts the engine, and the caravan drives away from the smoldering rubble.