In the inner courtyard, Tyreese explains to Rick, Carol and Daryl how he found Karen and David's charred corpses; He came to see Karen, saw the blood trail on the floor, and it led him outside, where he found that they had been murdered in cold blood. Tyreese demands Rick to find who did it and bring the killer to him; When the latter tries to calm him down, he turns violent and attacks Rick, punching him in the face twice. Daryl holds him back, and Carol tries to stop Rick from retaliating, but it's too late. Rick charges at Tyreese, knocking him down and brutally beating his face. Daryl eventually pulls Rick off of Tyreese before it can go any further. Rick looks at his severely injured hand, horrified at what he just did.
Dr. S and Hershel are looking over a bite victim, who got his arm amputated. Unluckily, the victim dies of blood-loss. Dr. S reluctantly prepares to put him down. Later, Hershel is seen bandaging Rick's hand. He comments on the group's situation, and that "everything they worked so hard to keep out just found its way in" and briefs Rick of the flu situation; It is spreading and that another council meeting is to be held the next day to make a final decision as to what they should do. Tyreese is seen digging graves for Karen and David. Bob approaches him, telling Tyreese to go see Hershel and make sure he's alright. Tyreese firmly says that he will, only after they are buried. Bob tries to change Tyreese's mind, but Tyreese glares at him and repeats "once they're in the ground." Bob then starts to help him dig.
Glenn suggests to Hershel that, with Karen and David dead, the infection may have been cured after all. Sasha suddenly leaves C-Block, coughing violently. She assures Hershel that she will go to A-Block - where all the sick people are being isolated - to see Dr. S, who is revealed to be sick as well. At the meeting the following morning, the council eventually reach the consensus that they need medical supplies in order to start the treatment. As Hershel mentions that there is an animal hospital facility nearby that could help, Glenn starts to show symptoms of the flu.
The sick are led into Cell Block A while Carol watches over them, wearing a mask for protection. Suddenly, Lizzie comes over and tells Carol that she is not feeling well. She asks if Carol can tuck her in, but Carol realizes that she might get infected. Heartbroken, Carol gives her a hug and sends her inside the cell-block to Glenn, before tearing off her mask and sobbing.
Outside, Carol is pumping the water, pointing out to Rick that they are running low. They agree that the next day they will go out to clean the cisterns. She suggests to Rick that he should talk to Tyreese, before leaving back to the prison. Rick cautiously approaches Tyreese who is finishing the graves. He says that he's sorry for hitting Tyreese, and then proceeds to ask him if Karen and David had any enemies or anyone who had a big problem with them. Tyreese fiercely denies this and then walks off, mocking Rick for spending the day "looking at water pumps" instead of trying to find the murderer.
In the cell block, Rick briefly talks to Carl to look over the office block, where the most vulnerable survivors are being kept at; the young kids and the elderly. Bob and Daryl fuel up a car, and Bob is disturbed when Daryl reveals that it was Zach's car. Back in A-Block Tyreese, who's there watching the sick (making sure no one will try to kill them), is asked to join the supply run for medical supplies with Daryl, Michonne and Bob. He refuses at first, but Daryl is able to convince him otherwise, saying he'll help them more in the run, looking for medicine than there, watching. He bids farewell to a sick Sasha, and leaves with the team.
In the office block, Hershel decides to go into the woods, hoping to find herbs (elder-berries) to treat the patients. After a tense moment with Carl, who insists that he go along with Hershel, they reach an agreement wherein Carl goes out with him. Outside, Hershel comments that he'd be good without him, and remarks how peaceful it is out there. How safe is out there compared to the Prison. Carl disagrees, pointing out to a nearby, severely-decomposed walker, and soon one more shows up. Carl prepares to shoot it, but Hershel stops him and tells him that he doesn't need to. Carl realizes this and they leave the place with the herbs (elder berries), with Carl remarking how peaceful it was.
Rick goes to the Tombs and investigates the courtyard. He examines the blood trail and takes a closer look at the door. There is a bloody handprint on the door and Rick compares the print with his own hand. He notices that it is relatively smaller that his own, suggesting that the killer may have been female. Rick sighs and glances away.
Arriving back at the prison, Maggie sees Hershel entering A-Block and warns him of the sick. Rick overhears the arguing and sides with Maggie. Hershel then proceeds to remind them of how they risk their life everyday and every hour, no matter what they do. He says that it isn't their choice; the only choice being what they are risking it for. Stating that he can help the sick, Hershel pulls a bandana over his face and goes into the cell block. He gives Dr. S the herb tea. Suffering heavily from the symptoms, he coughs blood which sprays onto Hershel's face. Aware that he's most likely infected already, Hershel takes off the bandanna and wipes his face. He also treats Glenn, giving him encouragement to keep pushing through.
Outside, Carol sets up a distraction for the walkers while she sneaks outside the fence to fix the clogged water intake hose. At the same time, several walkers emerge from the forest behind Carol, while at the same time, a few of the walkers at the fence turn their attention towards her. Rick notices this and runs towards her. Carol hurriedly attempts to finish, but drops the fitting into the pond. Rick comes to her aid just in time. They both run back towards the fences and make it back inside. Rick tells her that they agreed to fix the hose tomorrow. "We don't know if we'll get a tomorrow", Carol replies. Rick later confronts Carol in the courtyard, calling her actions from earlier 'moronic'. Carol halfheartedly agrees. As she begins walking away, Rick asks Carol if there's anything that she wouldn't do for the group. After she responds "no", he asks her if she killed Karen and David: After a moment, she replies calmly with a simple "yes."
While driving towards the hospital for the supply run, the group hears a voice over the car radio repeating the word "Sanctuary...Sanctuary...survive..." Daryl is distracted by it and hits a few walkers on the road. He stops the car, shocked at the massive herd of thousands of walkers between them and their destination. Daryl drives in reverse and runs over several more walkers, which pile up under the car, lifting the rear wheels and utterly immobolizing it. The rear tires spin, splattering blood and gore onto the side panels, forcing them to abandon the car. Daryl, Michonne and Bob make it out and hold their own, but Tyreese stays behind, seemingly in a stupor. Bob eventually snaps him out of it and Tyreese storms out of the car and in a rage, ferociously begins to kill the walkers that are quickly surrounding him, yelling at the others to go as he is surrounded. After running in the woods for a while, the group stops to rest, and notice movement in the bushes. Tyreese emerges, covered in walker guts and blood, but alive and unscathed. They keep moving, as the walkers chase after them.
- Tinsley and Anniston Price as Judith Grimes
- Randy Woods as Mr. Jacobson
- Brandon Carroll as David
- Corey Reitz as "Noris' Son"
- Sarah Wayne Callies as Lori Grimes (Photograph)
- Erin Hunter as "Crying Mom"
- Will Martin as "Sick Teenager"
- Becky Shaw as the "Achey Woman"
- Denny Ainsworth as "Woodbury Resident"
- Bill Vella as "Woodbury Resident"
- Deanna Dixon as "Woodbury Resident"
- Evelyn Elliott, Debra Svitil, Cory Robertson, Sarah Wildman & Hannah Moore as "Prison Survivors"
- Wallace Krebs as "Amputated Survivor"
- John Jaret, Jeff Matthew Glover, Christopher Kelly & Shellita Boxie as Walkers
- Taylor McPherson as Thomas (Due to a Filming Error)
- 2 unnamed prison residents
- First appearance of the Achey Woman.
- The name of the episode refers to the isolation of the survivors infected with the flu from the presumed uninfected young and old.
- The herd featured in this episode is the largest within the entire The Walking Dead media, including over 7,500 walkers.
- In a behind-the-scenes video on the AMC website, the VFX Supervisor mentions that they turned 100 real Zombie Extras into about 10,000.
- Carl is using the backpack that he, Rick and Michonne took from the Hitchhiker from Season 3, "Clear".
- This episode marks the first time we have seen Carol leave the prison since the group's arrival in "Seed".
- While Glenn and Maggie are digging graves in the Prison yard for the residents killed in the attack on Cell Block D, Thomas can be seen digging alongside them, despite dying in the attack in the previous episode. Because scenes are sometimes filmed out of episodic order, his presence was most likely an oversight by the crew of the show.
- The radio transmission is the first mention of Terminus. The next reference to it will be several episodes later, in Inmates.