Rick arrives back at the prison and meets Maggie who is busy clearing walkers from the fence. After Rick asks about Carl, Maggie questions him on Carol's whereabouts. After he avoids it with another question, she demands him to tell her. He tells her what happened to Carol, asking whether or not she'd do the same. After hesitance, Maggie agrees, but insists she wouldn't be able to actually commit to it. Rick tells her to follow her instincts before leaving. Rick heads to the administration building, where he gives a bag of food to Carl.
Inside A Block, things get worse when a few more members get sick. Henry cannot breathe and Hershel inserts a tube into his throat along with an air pump. Sasha and Glenn take shifts pumping air into his throat, beginning with Sasha. Glenn and Hershel find Mr. Jacobson dead with blood covering his face from his nose and mouth. Glenn attempts to kill him when Hershel warns him of not doing it in front of everyone. When they get him out of the Cell, Hershel is unable to put him down and Glenn does so. Later, Maggie comes to visit Glenn through the window, but Hershel tells her that Glenn is resting and tells her to stay out. When Hershel starts closing everyone's cell doors as Caleb had warned him to, a man storms out of his cell suffocating from the blood in his lungs. An extremely weak Sasha helps Hershel put him on a bed with wheels before she gets too weak to help him. He warns her to return to her cell and he brings the body into the room with the window. He fails to put the man down and has to cover his face before he can do it. Rick witnesses Hershel stab the man in the face and tells him of Carol.
When Hershel returns to the Cell Block, he continues closing cell doors. However, upon seeing a collapsed Sasha, he runs to her, leaving a cell with a female walker open. Hershel notices that Sasha has passed out, due to dehydration, and he revives her. She tells him of how she used to calculate everything to live as long as possible and that she is thankful for his "stupid" behavior. He then starts to close more cell doors when he spots Noris and his son passed out in the same cell. The father warns him that he wants to stay by his son's side and locks the cell door. Soon after, Glenn was pumping air for Henry, but he dies. When Glenn attempts to call out for help, he starts choking on his own blood and passes out. Lizzie finds him as the man starts to reanimate. Lizzie calls for help, which gets the attention of the female walker behind Hershel. The female walker jumps on Hershel and pins him to the ground. The father leaves his cell with a gun and his reanimated son follows him. A blonde woman comes to his rescue and pulls the walker off of Hershel, potentially saving his life. However, the father's son attacks his father from behind, to which he accidentally fires a gunshot that kills the woman. The gunshot echoes through the prison to Maggie and Rick who are fortifying the fence. Rick warns her to go help the people in Cell Block A.
Meanwhile, Lizzie leads the walker away from Glenn as Maggie arrives and attempts to open the door without success. Hershel gets up and runs toward Lizzie, who gets pinned by the walker. He manages to throw the walker off of the catwalk. He sticks Lizzie in Luke's cell and he goes to get the shotgun from Caleb, however he has already turned. Caleb grabs Hershel as the female walker starts to move up the stairs. With sadness, Hershel breaks one of Caleb's arms and kills him. He proceeds to kill three walkers after leading them out of the children's sight. He realizes he needs the air pump and climbs onto the metal fence that the walker from before landed. He ends up getting pinned. Maggie heads to the visitors room and smashes a window to get into A Block. She kills the reanimated father and the walker that pinned Hershel and the two head to help Glenn who has stopped breathing.
Outside, the fence gives way and a horde of walkers get in. Rick and Carl run into the courtyard, where they get assault rifles and gun down the many walkers. Right after they finish, the van with Daryl, Michonne, Tyreese, and Bob finally returns. Daryl and Michonne run out of the van to go help, while Bob and Tyreese head to A Block. Tyreese goes and cradles his sister in his arms, while Bob goes to administer drugs to Glenn.
The next morning, Rick returns to his usual routine, splashing water on his face. He is about to go talk to Daryl when Carl comes along. Rick instead decides to spend time with Carl harvesting the garden. Hershel helps Michonne and Daryl load up the dead bodies. Daryl asks where Carol is, and Hershel avoids the question by telling him that she is fine but to talk to Rick about her. Michonne extends an offer to Hershel to join her, and he accepts.
Outside, The Governor is seen observing the prison from a distance.
- Sherry Richards as Jeanette
- Jan Harrelson as Noris (Credited as "Father")
- Luke Donaldson as Luke
- Erin Hunter as "Crying Mom"
- Randy Woods as Mr. Jacobson
- James Keats as Henry
- Corey Reitz as "Noris' Son"
- Santiago Cirilo as Julio
- Will Martin as "Sick Teenager"
- Becky Shaw as the "Achey Woman"
- Denny Ainsworth as "Woodbury Resident"
- Leola Williams as "Woodbury Resident"
- Adam Daniels as "Prison Newcomer"
- Deanna Dixon as "Woodbury Resident"
- Sarah Wildman, Greg Rothstein, Hannah Moore as "Prison Survivors"
- Lauren Henneberg, Michelle Brannon, Greg Tresan, Shellita Boxie, Jerrad Vunovich & Ellie Decker as Walkers
- Mr. Jacobson (Zombified)
- Caleb Subramanian (Alive and Zombified)
- "Noris' Son" (Alive and Zombified)
- "Crying Mom" (Alive and Zombified)
- Noris (Alive and Zombified)
- Henry (Alive and Zombified)
- "Woodbury Resident" (Off-Screen)
- "Prison Resident" (Alive and Zombified)
- "Prison Resident" (Alive and Zombified)
- First appearance of Julio.
- Last appearance of Caleb Subramanian.
- Last appearance of Mr. Jacobson.
- Last appearance of Noris.
- Last appearance of "Noris' Son".
- Last appearance of "Crying Mom".
- David Morrissey (The Governor), makes his first appearance since the Season 3 finale, "Welcome to the Tombs".
- The title of this episode is referring to putting and keeping the infected into their prison cells or other kind of detention because someone (Hershel) thinks they might be dangerous. This is also done to prevent the sick from seeing the fate of those who succumbed to the flu. However, they already know what's happening, despite Hershel trying to hide it.
- The song featured in this episode is "Oats In The Water" by Ben Howard
- This episode takes place at the same time as "Dead Weight".
- This is the first episode since the Season 3 premiere episode "Seed", to show the prison yard during night time.
- This is the first (and currently only) episode in the series in which all known members of at least one family are killed off within the episode (as observed through Noris and his son).
- After Rick returns to the prison, while talking to Maggie, the Hyundai's driver's door is open, after a few shots, the passenger's door is open while the driver's door is closed. The two doors change from open to closed during the change of shots, until both doors are shown closed, but when Rick is walking back to the car, the driver's door is open again like in the beginning of the scene.
- When Rick bludgeons the walker with his rifle, he is clearly shown attaching a fresh magazine. It is also visible while he hits the walker. However, in the next shot, the magazine is missing and Carl throws him another one.
- When the prison survivors start turning into walkers and attacking cell block A, Maggie and Rick are outside chopping wood to hold up the fence when they hear the gunshot. It is daylight at this time. When Maggie runs off, Rick goes to find Carl to help him, but by this point it is suddenly pitch dark outside. Even though only minutes seem to have passed.
- When Rick and Maggie are reinforcing the wall, Rick's gun is holstered on his left side, rather than its usual place on his right.