After spending the winter on the run, Rick and his group of survivors come across an abandoned prison and kill all the walkers in a cell block, making it their home.
The prison group is attacked by walkers while exploring the lower levels. Hershel gets bitten, and Rick hacks off his leg to prevent infection.
The survivors then find a group of inmates who’ve been locked in the cafeteria for 10 months. Rick offers to clear a second cell block with them in exchange for food rations.
While clearing out the cell block, the inmates’ leader, Tomas, pushes a walker onto Rick. Rick kills Tomas, then fends off an attack by another prisoner, Andrew. Rick chases Andrew outside and leaves him for dead. The other two prisoners, Oscar and Axel, stand by Rick.
Andrea and Michonne are discovered in the forest by Merle Dixon, who now sports a bayonet prosthetic hand. He takes them to an idyllic town, Woodbury, where Andrea tells him his brother Daryl is still alive.
Andrea and Michonne meet the Governor, Woodbury’s leader, who welcomes them to stay as long as they like. Andrea wants to stay but Michonne mistrusts the Governor.
The Governor and his men track down a nearby military squad and gun them down, pilfering their weapons. Later, the Governor enters a room in his apartment and gazes upon a wall of aquariums containing live walker heads.
Amid the chaos, Lori goes into labor and begins to hemorrhage. Growing faint, she begs Maggie to cut the baby out. A tearful Maggie finally does so and Carl shoots his mother to prevent her from turning into a walker.
Maggie and Carl bring the baby out and rejoin the group. Rick collapses when he realizes Lori is dead. Graves are dug for those who fell, including Carol.
In his apartment, the Governor brushes the hair of his undead daughter, Penny.
Michonne discovers a cage of walkers in an industrial courtyard in Woodbury and kills them all. The Governor admonishes her, and Michonne decides to leave. Andrea stays behind.
The Governor’s “Research Team” retrieves walkers from a pit to replace the ones Michonne killed. That night, the Governor takes Andrea to a gladiator fight between Merle, Martinez and the captive walkers. Andrea calls it barbaric.
In a rage, Rick storms through the prison slaughtering walkers. He gets to the boiler room where Lori died and repeatedly stabs the walker that gorged on her. In a stupor, he hears a ringing phone and answers. He talks to various people, then sobs when he realizes one of them is Lori.
Meanwhile, Merle hunts down Michonne in the forest. She kills two of his men and flees into a walker-infested zone. Merle calls off the hunt and kills the remaining member of his team when he challenges Merle’s decision.
On his way back to Woodbury, Merle runs into Glenn and Maggie, who’ve gone on a run to look for baby formula. Michonne watches from a distance as Merle takes them hostage.
Michonne takes the baby formula to the prison, where she reports what happened to Glenn and Maggie and offers to help infiltrate Woodbury.
Daryl interrupts the debriefing to report that he found Carol dazed and dehydrated in an abandoned cell.
Back in Woodbury, Merle beats a bound Glenn and demands to know the whereabouts of his camp. He lets a walker loose in the room, but Glenn manages to break his shackles and kill it.
Next door, the Governor interrogates Maggie and orders her to remove her shirt and bra. He brings her into Glenn’s room and threatens Glenn’s life, forcing her to give up the prison’s location.
Andrea helps Milton, the Governor’s “advisor,” conduct an experiment to see if traces of human consciousness remain once someone has turned. Andrea kills the subject of the experiment when he lunges at Milton.
Newcomers Tyreese, Sasha, Ben and Allen take refuge in the prison when a member of their group, Donna, is bitten. Hershel takes them in but warns that Rick may not be as welcoming.
That night, Rick, Daryl, Michonne and Oscar sneak into Woodbury to rescue Glenn and Maggie. In the ensuing firefight, Oscar is killed and Daryl gets separated from the group.
Michonne sneaks into the Governor’s apartment, finds Penny and kills her. The Governor is enraged and they brawl, shattering the walker head aquariums. Michonne grabs a shard of glass and stabs the Governor in the eye. Andrea finds Michonne readying to kill the Governor and threatens to shoot her. Michonne flees.
The Governor gathers Woodbury’s citizens and explains the attack was the result of a betrayal. He brings out Merle and a captured Daryl and accuses them of colluding against Woodbury. Rick and Maggie fire into the crowd and rescue Merle and Daryl.
Rick’s group refuses to let Merle accompany them back to the prison. “No him, no me,” Daryl says, striding off into the forest with Merle. But it’s not long before Daryl tires of Merle’s bad attitude and declares he’s going back to the prison.
Andrea tries to calm frightened Woodbury residents and asks the Governor to reassure them. Instead, he gears up for war.
Back at the prison, Rick is about to let Tyreese’s group join when he suddenly hallucinates Lori in her wedding dress. “You don’t belong here!” he screams. Tyreese assumes he’s talking to them and leaves.
Hershel worries about Rick’s mental state and tries to talk to him. Rick admits he’s been hallucinating Lori. The Governor suddenly ambushes the prison, killing Axel and unleashing walkers into the yard. Daryl and Merle arrive just in time to save Rick from a walker.
After the assault, the Governor enlists Woodbury citizens aged 13 and older to fight. Andrea suggests they try to arrange a truce instead. “You go to that prison, stay there,” the Governor warns. He orders Milton to keep tabs on her.
Later, Andrea asks Milton to help her escape so that she can broker the truce herself. Milton tells the Governor, who instructs Milton to help her.
Milton escorts Andrea through the forest, where they run into Tyreese’s group. Milton takes them back to Woodbury while Andrea continues on to the prison, where she tells everyone that she wants to broker a peace. Rick’s group is dubious. Carol urges Andrea to have sex with the Governor and then kill him in his sleep.
Back in Woodbury, Milton introduces Tyreese’s group to the Governor. Tyreese offers to help in the fight against Rick.
Andrea returns to Woodbury and tells the Governor that she came back of her own volition. They have sex, but she can’t bring herself to kill him.
Michonne, Rick and Carl head to Rick’s hometown to look for guns. Carl privately expresses doubts about Michonne.
In town, they’re attacked by a sniper and knock him unconscious: It’s Morgan. In his apartment, they find a huge cache of weapons, which they load into their bags.
While Rick tries to reason with Morgan, Carl and Michonne visit a cafe to retrieve a family photo so that Judith can know what Lori looked like. They escape a swarm of walkers inside the restaurant.
Meanwhile, Rick learns that Morgan has become mentally unstable since the death of his son Duane. Rick tries to convince Morgan to join them but Morgan refuses.
As they pack up to leave, Carl tells Rick that Michonne is “one of us.”
Rick meets the Governor in an abandoned feed store to negotiate. The Governor demands Rick’s surrender but offers to stand down if Rick turns over Michonne. He gives Rick two days to decide.
Back in Woodbury, the Governor orders his men to kill Rick’s group. “What about the deal?” Milton asks. “No way we can all live side by side,” the Governor says.
At the prison, Rick announces they’re going to war. Privately, he tells Hershel about the Governor’s offer, hoping, he says, “that you can talk me out of it.”
Milton tells Andrea about the Governor’s plan to kill Rick’s group. Andrea sneaks out to warn Rick.
Martinez enlists Tyreese’s group to round up walkers at the pit. Tyreese refuses to participate once he realizes that the plan is to unleash them on the prison group.
The Governor chases Andrea in his truck and corners her at an abandoned warehouse. She escapes but is later captured at the prison perimeter. The Governor ties her up in Woodbury’s interrogation room, which he’s converted into a torture chamber.
Milton lights the pit walkers on fire and tries to hide the fact from the Governor the next morning.
Meanwhile, Rick asks Merle to help kidnap Michonne. But after suffering another hallucination of Lori — this time, standing pregnant on the catwalk — he backs out.
Merle, anticipating Rick’s change of heart, kidnaps Michonne himself. Michonne convinces Merle to release her, but he refuses to go back with her. “There’s somethin’ I gotta do,” he says.
Merle lures a group of walkers to the feed store and fires at the Governor’s men. The Governor discovers Merle and shoots him dead. Daryl later finds Merle as a walker and tearfully stabs him to death.
Glenn proposes marriage to Maggie and she accepts.
Rick discloses the Governor’s offer to the group but says he couldn’t sacrifice Michonne.
The Governor stabs Milton in retaliation for killing the pit walkers and leaves him slowly bleeding to death in the torture chamber with a bound Andrea.
Afterwards, the Governor and his soldiers storm the prison, only to find it empty. As they search the maze of hallways known as The Tombs, a smoke grenade goes off and the alarm sounds, drawing walkers. The Governor’s soldiers run outside, where Glenn and Maggie open fire. They flee.
Back in the torture chamber, Milton tells Andrea he left a pair of pliers near her feet. As she struggles to cut herself free, Milton dies and turns into a walker.
Rick admonishes Carl for shooting a defenseless Woodbury boy that was trying to run away, but Carl says he couldn’t risk a potential threat to their safety.
On the road back to Woodbury, the Governor stops his caravan and screams at his soldiers for retreating. When they refuse to go back, he opens fire, killing them. Then he drives off with Martinez and Shumpert.
Rick, Michonne and Daryl discover the Governor’s massacre and continue on to Woodbury, where they find Andrea has been savagely attacked by Walker Milton. With Michonne at her side, Andrea shoots herself.
Rick shuttles the rest of the Woodbury survivors back to the prison. “They’re gonna join us,” he tells Carl.
Rick looks up at the catwalk. Lori is nowhere to be seen.