The episode begins right outside of the prison perimeter. The sun is setting, and a woman's screams can be heard in the woods. Two walkers are walking towards the sound of the screams. Suddenly, a man named Tyreese comes out from behind a tree and kills the two walkers with a large hammer. He runs through the forest and comes upon a woman, his sister named Sasha. Sasha asks Tyreese if he is alright. Tyreese states that he is, but tells her that they need to keep moving. Sasha states that she lost the others a little ways back. Tyreese states that he thinks he found a building while he was scouting ahead and they need to get to it. The two look back and see that Allen, Donna, and Ben, a family, are being swarmed by the walkers. They are able to kill several of them, and Tyreese calls for them to follow him. The five run into the woods, but are still being chased by the walkers. Unfortunately, one of them grabs Donna and bites her on the arm. Allen kills the walker, and helps Donna get away so she doesn't get hurt further. The five make it to the rear entrance of the prison. The fence is down on one side of the prison and part of a building has been destroyed, leaving an opening for people and walkers to get into. The group is unsure about whether to enter, but Tyreese knows that there is more danger outside with the walkers surrounding them. Sasha tells Allen that they need to leave Donna outside since she's been bitten because she's going to slow them down. Donna states that she'll stay outside. Allen protests, stating that the walkers will tear her apart. Tyreese objects to leaving Donna outside, noting that Ben needs time to say goodbye to his mother and not wanting to see Donna die in a horrible way. Sasha thinks it's a mistake, but she relents and the five of them enter the prison.
In Woodbury, Andrea looks at the Governor's picture of his family. Andrea tells the Governor that she's going to help Milton cremate Mr. Coleman's body. The Governor notes that Andrea doesn't have to help if she's still rattled from the experience. Andrea states that Milton shouldn't have to do it alone. She notes that everyone inside Woodbury is here to help everyone through the mess that's been created by the zombie apocalypse. The Governor asks Andrea if Woodbury is growing on her. Andrea states that it is, and kisses the Governor.
The Governor later goes into his room and starts playing music. The walker heads are still moving in the fish tanks and he calls for his walker daughter, Penny, to come outside. Walker Penny runs out of the room, but she is strapped to a chain. The Governor takes off her mask and tries to get her to recognize him. He starts to sing the song, which was probably one of Penny's favorites when she was alive. However, Penny doesn't recognize him. The Governor yells at her to remember, but gets frustrated and puts her back in the closet.
Glenn and Maggie are still imprisoned inside a room. Glenn asks Maggie if the Governor raped her. Maggie insists that he didn't, and states that the Governor barely touched her. Maggie states that she forgot about what people can do to other people since they've been running from the walkers. Glenn agrees, but is glad that Maggie is alright. He hugs her tightly. Glenn looks over at the walker body and then rips the arm off. Maggie looks in horror as Glenn pulls one of the walker's bones out of the body. He hands one to Maggie. The two have weapons that they can use against the Woodbury guards.
Rick, Daryl, Michonne, and Oscar look at the wall and try to find a way inside. Suddenly, Michonne breaks from the group and goes somewhere else. Rick yells at her to come back, but she is gone. Daryl notes that they aren't going to be able to check all of the buildings with the guards around. Suddenly, Michonne comes back and tells them to follow her.
The Governor tells Merle that Rick's group was smart in taking the prison, noting that it keeps the walkers out. Merle asks if it's wise to move Woodbury. The Governor states that Woodbury makes people feel like things are normal, whereas a prison would be terrible conditions. The Governor states that he just wants the other group to move out so the biters can invade it again. Merle notes that Daryl is with that group. The Governor notes that Merle can talk to Daryl and make him the inside man. The Governor states that they'll drive up waving the white flag and then take everyone out. Merle states that nothing can happen to Daryl. The Governor promises that Daryl would be safe. Merle asks the Governor what they should do with Glenn and Maggie. The Governor notes that they don't want Andrea to find out they are here, and tells Merle to take them to the pits.
Rick, Daryl, Michonne, and Oscar have found a way to secretly breach the walls. They arrive inside one of the buildings. Michonne states that she was questioned in this room when she first arrived to Woodbury, but Glenn and Maggie are not there. Daryl notes that there are armed sentries moving around the streets. Rick notes that if anyone comes in here and sees them, they would be massacred. Michonne wonders if they are in the Governor's apartment. Daryl asks where they would be if they aren't. Michonne states that they could be anywhere. Rick is upset noting that Michonne said that she could help. Michonne states that she's doing the best she can. Oscar tells her that she needs to start thinking. Rick pulls the other two aside and notes that if Michonne doesn't help, they're cutting her loose. Oscar worries that Michonne might be leading them into a trap. Daryl states that they could split up. Suddenly, the door opens, and one of the guards comes inside. The guard calls out, stating that he knows someone is in here, but he doesn't realize that it's outsiders. He thinks it's someone from Woodbury snooping around. Suddenly, Rick pounces on him and orders him to the ground. Rick asks the man where Glenn and Maggie are. The man insists that he doesn't know. Rick realizes the man doesn't know anything and gags his mouth. Daryl knocks him out and they drag him away from sight.
At the prison, Axel tells Beth that she's very good with Judith. He starts to ask her questions about her age and her history. Carol thinks he has bad intentions and asks him to come with her. Carol tells Axel to stay away from Beth. Axel states that he wasn't going to harm Beth. Carol tells him that he shouldn't be out to try and repopulate the earth through Beth. Axel states that he didn't mean to offend her. He admits he's been locked up for a long time and hasn't seen a woman for years. Axel notes that there aren't many available women left in the world. He knows that Maggie and Glenn are together, and he tells Carol that she's a lesbian. Carol tells him that she's not a lesbian. Axel gets his hopes up and thinks that maybe he has a shot with Carol. Carol turns him down.
Merle and another guard, Warren, go to take Glenn and Maggie to the pits. When they open the door, Glenn lunges at Merle. Maggie is able to grab onto Warren and stabs him in the throat with the walker bone, killing him. Before Warren dies, his body jerks his Uzi, which causes bullets to spray everywhere. Rick and the others hear the gunfire. Maggie gets a hold of Merle's gun, but Martinez and some other men come into the room and hold guns on her. Maggie realizes she is outnumbered and drops her gun.
Rick and the others arrive near the spot where the gunfire was heard. Glenn and Maggie have sacks put around their heads and are being lead out to the pits. Rick throws a tear gas grenade that explodes and showers the room with smoke. Rick and the others grab Glenn and Maggie, and lead them away from Merle and the others. Andrea hears the gunshots and tells the Governor she can help with the problem. The Governor tells her to stay away from the area, stating that it's just walkers. A woman yells for help, and they find the guard that was knocked out. He tells them about being knocked out by some people that invaded Woodbury. Everyone worries that Woodbury is under attack. The Governor tells everyone to go inside and lock their doors. He promises that everything will be alright. The Governor tells his soldiers to find the intruders and kill them if they have to.
Rick, Daryl, Oscar, Michonne, Glenn, and Maggie take cover inside of a building. However, Michonne shuts the door, and goes off somewhere else. Glenn and Maggie are grateful that Rick came for them, and they notice that Michonne disappeared. Rick states that Michonne is on her own, and they need to leave. Glenn informs Daryl that Merle was the one that did this to them. Daryl can't believe his brother is alive and asks him if Merle is the Governor. Maggie states that the Governor is a different person, but Merle is a lieutenant. Daryl asks them if Merle knows he's still alive. Glenn states that Merle and the Governor know everything, and apologizes to Rick for giving up the prison. Rick tells him he has no reason to apologize. Maggie notes that everyone is going to be looking for them. Rick states that they need to leave now. Daryl states that if Merle is here then he needs to see him. Rick states that they are in hostile territory and they can't risk their lives to go see Merle. Rick notes that Merle harmed Glenn and tried to kill him. Daryl thinks that he can work something out with Merle and he wants to see him. Rick tells Daryl to think clearly, noting that he needs his help to get Glenn to safety. Daryl tells Rick that he's with him.
The Governor, Merle, Milton, Martinez, Andrea, and Shumpert meet in a room to discuss their plan of action. They all know that the wall has been breached and people have made their way into Woodbury. Merle tells the other that Warren was killed after being stabbed. The Governor states that they need patrols. He tells Andrea to go door to door and make sure that everyone is safe. Andrea doesn't want to be stuck with a menial task. The Governor notes that the intruders may have taken people hostage and Andrea could save someone. Andrea states that someone else can do the job, noting she has firearms experience. The Governor tells her that she has her job, and tells Merle to lead the search for the intruders. Andrea tells the Governor that Haley can search door to door, insisting that she is good with a gun. The Governor tells Andrea to do what he asked her to do. Andrea relents and agrees to go door to door.
Michonne goes inside the Governor's apartment, hoping he is there. She finds it empty, but sits on the chair in the living room, waiting for him to come back.
Rick and the others prepare to fight their way out of Woodbury. Daryl throws a tear gas grenade and they all run under the cover of the smoke. Rick shoots one of the Woodbury guards on the wall and Daryl shoots another one. Andrea finds the shooting and she runs over to help the others. Rick and Daryl both kill another Woodbury soldier each and the five run for cover. The Governor runs to the scene and asks Andrea if she's alright. Andrea states that she saw the intruders. Andrea tells the Governor that the intruder she saw was wearing a prison jumpsuit. The Governor tells her it must be escaped convicts causing mayhem. He tells her that they need to clear the streets. Daryl tells the others that he is going to lay cover fire so everyone can get over the wall. He throws another tear gas canister and the others run for cover. Rick helps to back them up. Oscar helps get Glenn over the wall. While Rick is firing, he suddenly sees an image of Shane with a beard and a shotgun coming towards him. Shane fires at them, and the blast hits Oscar in the torso, knocking him down. Rick breaks from cover and shoots Shane right in the face. However, when he walks up to the man, he sees that it isn't Shane, as Shane is dead. It's just another guard from Woodbury that he killed. Rick realizes that he's seeing things again. Maggie checks on Oscar, but finds that he is dead. She shoots him in the head to prevent him from coming back as a walker. Daryl stays behind to provide cover fire while Rick, Glenn, and Maggie get over the wall.
Back at the prison, Beth and Carl are loading cartridges for the guns. Hershel tells Carl that he finally got Judith to sleep. Carl asks if they have enough formula. Hershel states that Judith will have enough formula for at least a month. Carl states that he'll take Carol and go get some more next week. Beth tells Carl that Rick and the others will be back soon. Carl states that they don't know that, and they have to be prepared for the worst. Suddenly, the groups hear a woman screaming. They realize the sound came from inside the prison, and it's not Carol, as she's outside on guard duty. Beth wonders who is making the sound, noting that the prison is secure. Hershel tells Beth that the tombs are filled with walkers, and that means there is a breach somewhere in the prison. Carl states that he's going to go investigate. Hershel tells Carl that he can't let him go. Carl states that his father would go, and he has to help whoever's down there.
Carl takes a flashlight and his silenced pistol down into the tombs. He looks around and follows the sounds of someone crying. He sees several dead walker bodies as he goes along. He passes by the boiler room, and remembers where his mother died. Suddenly, a walker appears behind Carl, but he shoots it. Carl walks into the boiler room and finds Tyreese, Sasha, Allen, Ben, and Donna. Tyreese and Sasha are fighting off the walkers while Allen tends to a dying Donna. A walker almost gets Sasha, but Carl shoots it. The group notices Carl and he tells them to follow him. The group listens and runs in Carl's direction. Sasha sees that Allen and Donna are slowing down as Donna is weak and near death. Tyreese runs back to pick up Donna since Allen has been carrying her and Sasha kills a walker to cover the others. Carl shoots another walker, and tells them that they have to leave Donna behind. Tyreese tells Carl that they don't leave their people behind, and he punches another walker. Carl shoots it, and the six run back to C Block.
Michonne still waits for the Governor to come inside when she hears a thumping noise behind one of the doors. Michonne goes to investigate, and that's when she walks into the room where the walker heads in the fish tanks are. She spots Welles' severed head in the top tank and all of the other heads. She is sickened by the sight of the fish tanks. Suddenly, she hears a noise coming from the closet. She looks inside and finds Walker Penny inside. However, Penny has a mask over her head so Michonne doesn't realize she's a walker, and thinks it's a little girl. Michonne tells the girl to come to her, promising that she won't hurt her. However, when she removes the mask and takes off the chain, she realizes that Penny is a walker. She prepares to stab her to put her out of her misery, but the Governor has returned. He points a gun at Michonne, and Michonne holds Penny hostage. The Governor puts his gun down, and begs her not to hurt Penny. The Governor tells Michonne that there is no need for Penny to suffer. Michonne states that Penny is a walker and doesn't have needs. The Governor begs Michonne not to hurt Penny. Michonne doesn't listen and stabs Walker Penny in the head. The Governor flips out and attacks Michonne. The two wrestle each other on the ground, trying to strangle each other and punching each other. At one point, the Governor gets the upper hand and throws her through one of the fish tanks. The severed heads try to bite at Michonne, and she throws several of the fish tanks on the ground, which causes the two of them to fall. The Governor grabs Michonne and tries to feed her to one of the severed heads. Michonne gets away and tries to grab her sword. It's not within reach, but she sees a large shard of glass in one of the fish tanks. She reaches for it, and painfully loosens it. After she does, she stabs the Governor through his right eye, blinding him in that eye and causing him severe pain. The Governor writhes on the ground in pain. Michonne is prepared to kill the Governor when Andrea comes in and points her gun at her. Andrea asks Michonne what she's done. Michonne stands and has her sword pointed at Andrea. The two standoff for several moments, but Michonne lowers her sword. She leaves the room. Andrea doesn't have the heart to shoot her. Andrea tends to the Governor and then looks around at the severed walker heads that are sitting in the fish tanks and on the floor. The Governor goes to his dead daughter and holds her tight, crying. Andrea doesn't know what to make of the entire scene, but she kneels down with the Governor while he mourns Penny's death.
Carl leads Tyreese's group into C Block. Allen realizes that Donna has died and sobs over the loss of his wife. Carl tells the others that he can take care of Donna. Tyreese tells him that he doesn't have to. Sasha asks Carl who he is and how he got into the prison. Carl tells Sasha that he can help them, but they need to take care of Donna. Tyreese tells Carl that they take care of their own. Allen tells Tyreese that he'll do it, but Tyreese doesn't want Allen to have to put down his own wife. He tells him to take care of Ben. Allen agrees and kisses his wife goodbye. They put a cloth over her face so Tyreese can kill the brain. Carl closes the cell door, locking them in the common area. Sasha tells Carl to open the door. Carl tells them that they will be safe and secure in that room, noting that they have food and water. Sasha again tells Carl to open the door, telling them that they are not animals. She's angry to be locked inside, but Tyreese tells Sasha to calm down and stop hitting the cell door. Tyreese tells Sasha that they are safe in this room and it's their house. Tyreese notes that they have other business to do. Tyreese tells Carl that they don't want any trouble. Beth asks Carl if they should help them. Carl states that he did.
Dr. Stevens treats the Governor's eye. She tells him that there is a lot of damage and he probably won't be able to see out of it. The Governor is too raged to care and tells her that he needs to leave. Andrea asks Dr. Stevens to give them a minute. Andrea asks the Governor why he was fighting Michonne. The Governor states that Michonne came back to kill him. Andrea doesn't understand why Michonne would want to kill him. The Governor notes that Michonne was Andrea's friend, so she must know the reason why. Andrea notes that she saw the fish tanks and the heads. The Governor states that he put the heads in the fish tanks so he could look at them every day and prepare himself for the horrors outside the walls. Andrea asks the Governor why he kept Penny after she became a walker. The Governor doesn't answer. Milton comes into the room and asks if he's alright. Merle comes in as well and asks what happened. The Governor gives Merle a sinister look and tells him that he was attacked. Merle tells the Governor that he will give chase first thing in the morning. The Governor continues to stare angrily at Merle, knowing that he lied about killing Michonne.
Rick, Glenn, and Maggie wait outside for Daryl to return. They hear rustling in the leaves and Michonne returns. Rick asks Michonne where she was. Michonne doesn't answer, and Rick takes her sword away from her. He asks her if she got what she was looking for. Michonne doesn't answer and asks if they rescue all of their people. Rick states that they got Glenn and Maggie back. Glenn is angry that Oscar was killed and tells Michonne what happened. Maggie asks Michonne if she saw Daryl. Rick tells Michonne that, for her sake, Daryl had better be alright. Michonne states that she held up her end of the bargain by bringing them to Woodbury to save Glenn and Maggie. Rick thanks Michonne for her help. Michonne tells Rick that she's still needed, noting that she can help them get Glenn back to the prison and to find Daryl. Rick realizes that he does need Michonne.
Everyone in Woodbury gathers at the arena to hear the Governor speak. The Governor tells everyone that this is the first incident that has happened since the walls went up. He admits that he thought they were safe inside of the walls and that they had a good thing going with Woodbury. The Governor tells his people that he failed them. The Governor states that he could tell them that everything is going to be alright, but he states that he can't do that this time. He admits to everyone that he is afraid. The Governor states that he's afraid that terrorists are going to destroy them, and notes that one of the terrorists is one of their own town's residents. The Governor states that Merle is the traitor. The Governor states that Merle was the one who led the terrorists inside of the prison. The Governor tells Merle that he lied to him about Michonne, and he betrayed everyone in the town. Suddenly, a man is brought out and revealed to be one of the terrorists. The Governor reveals the man is Daryl, and he tells everyone that Daryl is Merle's brother. Daryl notices Andrea standing in the crowd. The Governor asks everyone what they should do with the traitors. The crowd yells that they should kill them. Andrea doesn't say anything, not knowing what to do in this situation. Daryl and Merle stare at each other worriedly. The Governor tells Merle that he wanted his brother badly, and now he has him. The episode ends with the crowd continuing to yell that they should kill Daryl and Merle.