Peace thrives at the prison as newcomers arrive on a regular basis. Having retired his gun, Rick cultivates a farm with crops and livestock.
Rick and Carl discover that the farm pigs are sick. Meanwhile, survivors take turns manning the perimeter fence, where walkers pile up in increasingly large droves.
While checking snares, Rick meets a stranger named Clara and considers letting her into the prison. However, she tries to kill Rick, to feed him to her undead husband. Afterward, Clara stabs herself and begs Rick to let her turn.
Daryl leads a group to a department store to stock up on supplies. Bob, one of the newcomers, stirs up a nest of walkers when he grabs a liquor bottle and topples a rotted shelving unit. Beth’s boyfriend Zach is killed in the attack.
In the prison library, Carol secretly teaches children how to use knives for protection. Patrick, one of the teenagers, feels sick and asks to be excused.
Later, Patrick dies and turns in the middle of the night. He tears out the throat of a sleeping occupant in D block, setting off a chain reaction of walker attacks. Rick and his crew rush over and kill the walkers in the cell block, but several people are dead or injured. Afterwards, Carol promises one of the dying victims that she’ll look after his daughters, Lizzie and Mika.
Noting that one of the victims turned without being bitten, the group deduces that the sick pigs are spreading a virus. The Prison Council quarantines all residents exhibiting symptoms.
Lizzie mourns the death of a walker she named Nick. “She’s messed up,” Mika tells Carol.
Tyreese goes to visit his girlfriend Karen, who’s fallen ill, but she’s missing. He follows a trail of blood to the prison yard and discovers the charred bodies of Karen and another survivor, David. Rick eventually confronts Carol about the murders, and she confesses.
Daryl, Michonne, Bob and Tyreese set off to find antibiotics and anti-viral medication at a nearby veterinary college. En route, Bob admits to Daryl that he’s an alcoholic.
The group scores the meds at the vet school. But Bob nearly dies when he refuses to let go of his backpack during a walker attack. Daryl is furious when he discovers that Bob was transporting liquor instead of medicine.
Rick takes Carol on a supply run, during which Carol explains she had to kill Karen and David to keep the outbreak from spreading. Rick exiles Carol from the prison, leaving her behind with a car and supplies.
At the prison, more victims succumb to the virus. Outside, walkers break down the perimeter fence and stream into the prison yard. Rick and Carl team up to shoot them down.
As an infected Glenn teeters on the brink of death, Daryl and his crew return with the meds. Everyone is treated.
In a flashback, the Governor is abandoned by Martinez and Shumpert after slaughtering the Woodbury residents. He wanders alone for months, then settles down in an apartment building with sisters Tara and Lilly Chambler; their father, David; and Lilly’s daughter Meghan.
Pretending his name is Brian, the Governor grows close to the family. When David turns after dying from lung cancer, the Governor bashes his head in, terrifying Meghan. The Governor decides to leave, but Lilly insists he take them along. He and Lilly begin a romance.
On the road, they run into Martinez, who has started his own camp. The Governor assures Martinez that he’s a changed man but later kills Martinez and takes over the camp.
The Governor fortifies the camp, but after a walker nearly kills Meghan, he decides to find a safer location. The next day, the Governor scouts out the prison.
The Governor kidnaps Hershel and Michonne and tells his camp that Rick’s people are the enemy. Despite Lilly’s opposition, he outlines a plan to take over the prison.
The Governor arrives at the prison with his army. Rick invites them to live together in peace, but the Governor responds by decapitating Hershel. Lilly then walks up to the Governor carrying Meghan: She’s dead, killed by a walker back at camp. The Governor shoots Meghan in the head and then orders his army to take down the prison fences and “Kill them all.”
Rick’s group scatters as they fight the Governor’s army. Rick pummels the Governor, who is later shot dead by a devastated Lilly. Walkers stream through the broken fences and flood the prison.
Rick and Carl flee into the woods and stop to rest at an abandoned house. Gravely injured, Rick falls unconscious. Carl, angry at his father for their predicament, goes off to scavenge alone. When Rick finally wakes, Carl admits he’s scared.
Michonne wanders through the woods alone. She has a nightmare about her dead boyfriend and toddler son. When she tracks Rick and Carl to the house, she bursts into tears of happiness.
Lizzie and Mika hike through the woods with Tyreese, who carries Judith. They run into Carol and follow nearby railroad tracks to a map and sign guiding survivors to “Terminus,” promising “sanctuary for all.”
Elsewhere, Maggie and Bob decide to find Glenn. Sasha, focused on finding a safe shelter, reluctantly agrees. They find the walker-infested prison bus on which Glenn was last seen, but he’s not there. They encounter a sign for Terminus and head toward it.
Back at the prison, Glenn teams up with Tara to escape. Tara, guilt-ridden over her role in attacking the prison, agrees to help Glenn find Maggie.
On the road, Glenn and Tara meet Sgt. Abraham Ford and his comrades, Rosita Espinosa and Dr. Eugene Porter. Abraham explains they’re en route to D.C., where Eugene, a scientist with knowledge about the walker outbreak, will be able to work on a cure. When their truck is destroyed in a walker attack, Abraham’s crew joins Glenn and Tara.
While recuperating at the house, Rick hides from a gang of violent men and strangles one of them to death. He escapes the house with Carl and Michonne. At the railroad tracks, they find a Terminus sign and decide to go.
Beth embarks on a mission to find alcohol. Daryl takes her to a cabin with a moonshine still. They drunkenly talk about escaping their pasts and burn down the cabin as catharsis.
Later, they discover a pristine funeral home and dine on food from its well-stocked cupboards. Walkers attack. Beth flees outside while Daryl leads the walkers downstairs. He escapes just in time to see a car race off with Beth inside.
Daryl chases after the car until he collapses, exhausted, by the railroad tracks. A gang — the same one Rick encountered — surrounds him. Daryl impresses the ringleader, Joe, with his crossbow, and they reach a detente.
Carol, Tyreese, Lizzie and Mika stay at a house in a pecan grove. Carol sees Lizzie playing with a walker in the yard. She kills it, angering Lizzie, who insists the walker was her friend. Lizzie vows to make Carol understand that walkers are people, too.
Carol and Tyreese return from hunting to find Lizzie standing over Mika’s dead body with a bloody knife. Carol takes Lizzie into the woods and shoots her.
That night, Carol admits to Tyreese that she killed Karen and David. Tyreese contains his anger and forgives her. They leave the house with Judith.
Daryl fights with Len, one of Joe’s gang members, over a rabbit he killed in the woods. Joe gives them each half the rabbit and explains the gang rules to Daryl: Say “Claimed” and the item is yours. He adds that lying and stealing are punishable by death.
Len later plants his half of the rabbit in Daryl’s bag and accuses Daryl of stealing. The gang beats Len to death for lying. Later, Joe tells Daryl they’re tracking down a man who strangled one of their own.
Glenn’s group finds a map to Terminus as well as a message from Maggie to meet them there. Abraham’s crew parts ways with Glenn and Tara when they reach a tunnel filled with walkers.
Inside the tunnel, Glenn tries to rescue Tara after her leg gets caught in rubble. As walkers begin to overtake them, a car pulls up and six figures gun the walkers down: Abraham’s crew has joined up with Maggie’s group after running into each other on the tracks. Glenn sees Maggie and they embrace.
Glenn, Maggie and the others reach Terminus. Inside, a woman named Mary welcomes them and offers them food.
In a series of flashbacks, Hershel convinces Rick to become a better role model for Carl by starting a prison farm.
In the present, Rick, Carl and Michonne set up camp by an abandoned truck. Joe and his gang surround them. The gang turns on Daryl when he comes to Rick’s defense. Rick bites a chunk out of Joe’s neck then stabs Carl’s assailant repeatedly.
Rick’s group reaches Terminus. Inside, a man named Gareth welcomes them and escorts them to a courtyard, where Mary prepares food.
Rick notices Terminus residents in possession of items that belonged to Glenn and the others. He confronts Gareth and a shootout ensues. Rick’s group flees but is eventually captured and herded into a train car. Inside, they find Glenn, Maggie and the others.
“They’re gonna feel pretty stupid when they find out,” Rick vows to the survivors, “they’re screwing with the wrong people.”