"Killer Within" is the fourth episode of the third season of AMC's The Walking Dead. It is the twenty-third episode of the series overall. It premiered on November 4, 2012. It was written by Sang Kyu Kim and directed by Guy Ferland.
An unidentified person wearing prison garb brings in a gas can and a deer corpse, dragging it into the prison. The unidentified person then tosses rocks at a couple of walkers to obtain their attention. The walkers feast on the deer carcass that has been strategically spread out to lure the walkers towards the prison gate. The person then breaks open the prison gate, placing the deer's heart in front of it.
The survivors are discussing plans to clear out the prison yard when Axel and Oscar approach, begging to join their group. T-Dog is in favor of allowing them, but many within the group disagree, expressing their concerns. Finally, Rick insists that they stick to their agreement, and the prisoners must stay in their cell block, or leave the prison.
In Woodbury, Michonne inspects the salvaged National Guard trucks, noticing bullet holes and traces of blood. She questions the Governor about the circumstances of the soldiers' deaths. He dodges her suspicions and attempts convincing her and Andrea to stay in Woodbury.
Back at the prison, Rick instructs Glenn to give Axel and Oscar a week's worth of supplies and send them on their way. Axel tries to ingratiate himself with Daryl by offering to tune his motorcycle, but Daryl ignores him. Meanwhile, Beth and Lori leave the safety of Cell Block C, assisting Hershel in getting comfortable with his crutches.
In their room, Michonne and Andrea discuss plans to head for the coast after leaving Woodbury. "I'd rather take my chances out there than stay here," Michonne declares. "Because your gut tells you there's something off about this place, about the Governor?" Andrea asks. Andrea must decide to trust Michonne's instincts, which have helped keep them alive all winter, or try to learn more about the Governor and Woodbury.
As Rick and the others clear the yard, Lori, Carl, and Beth escort Hershel outside. The group rejoices at Hershel's recovery, and Rick and Lori share warm looks from a distance, causing Lori to blush. However, the warm moment is interrupted as a group of walkers suddenly flood the courtyard. Gunfire erupts as Rick, Daryl, and Glenn race to join the fight. Hershel and Beth lock themselves in a fenced-in entryway while Maggie, Lori, and Carl flee into the cell block. While resealing the courtyard gate with Carol, T-Dog is bitten on the shoulder by a walker before he and Carol flee to safety inside the prison.
Back in Woodbury, Andrea reveals to Merle the location of Hershel's farm so he can search for Daryl. When she declines his offer to join, he remarks that they were both abandoned — and then rescued — by the same two groups of people. Andrea asks Merle if the Governor is a good man. "I wasn't in the best of shape when he found me," Merle replies. "He should've just kept on going. Yeah. He's a good man."
In the prison yard, Glenn reports that someone had cut the gate open. When Axel and Oscar approach, Rick accuses them. Just then, the prison's alarm sounds, attracting more walkers to the outer fence. Oscar explains the back-up generators must be powering it — proving that someone else is messing with things from inside the prison — and follows Rick inside to disable them.
Wandering the prison hallways, Carol offers to "do whatever's necessary" to help T-Dog with his bite, but he insists on guiding her back to the cell block before he dies. Lori, Carl, and Maggie are also wandering when the stress of the situation causes Lori to go into labor. Carl leads them into the boiler room.
Meanwhile, Merle discusses leaving to search for his brother Daryl using the information that Andrea provided. The Governor says he can't risk losing Merle on a wild goose chase, but agrees to help him search for Daryl if he can obtain more concrete information.
Back at the cell block, Rick, Daryl, Glenn, Axel, and Oscar separate into teams to look for the others and shut down the back-up generators. In the boiler room, Maggie assists Lori in removing her pants and gets her ready to deliver the baby naturally. Carl stares at them in confusion and horror. But as Lori pushes through her contractions, she begins to hemorrhage.
T-Dog and Carol reach the laundry room doors, but their path is blocked by two walkers. Out of ammo, Carol looks to turn back, but T-Dog, knowing that he is already doomed, charges at them, pinning them against a wall, urging Carol to keep going. She reaches the doors, but looks back in horror and sadness as the walkers begin to devour T-Dog.
Back in Woodbury, Andrea and the Governor share a parting drink in his apartment, where he reveals his real name — Philip — and that his wife died in a car accident before the apocalypse. Andrea reveals that she isn't sure what she wants anymore. Before she leaves, the Governor tells her that she is welcome to return to Woodbury anytime. Andrea tells Michonne she wants to stay longer but Michonne doesn't want any part of it, and storms out.
Rick, Oscar, and Daryl reach the generator room, where they find Andrew — still alive and waiting to attack them, revealing that he lured the walkers and caused the attack as his revenge. As Andrew and Rick struggle, Oscar throws a barrel which hits Andrew in the head and picks up Rick's gun. The two men stop fighting and Oscar aims his weapon at Rick. Andrew urges him to shoot Rick, but Oscar changes his mind, and decides to shoot Andrew in the head instead, returning the pistol he is holding to Rick. Rick powers down the generator.
In the boiler room, Lori grows faint as the hemorrhaging continues. She realizes she will not survive natural childbirth. "I'm not losing my baby," she tells Maggie. "You've got to cut me open." Lori tearfully says goodbye to Carl, telling him that he is smart and strong, and that he has what it takes to survive the apocalyptic world. "Don't let the world spoil you," she says. "You're the best thing I ever did." Maggie reluctantly slices Lori's abdomen open and scoops the baby out. The baby survives, but Lori lays motionless, blood pouring from her open wound. Maggie starts to leave with the baby when Carl stops her. "We can't just leave her here," Carl says. "She'll turn." Carl insists on perform the coup de grâce as the son. Maggie moves away and hears a gunshot. Carl walks briskly past her towards the exit.
Rick, Daryl, Axel, Oscar and Glenn move through the prison, taking out a pair of walkers, and discovering T-Dog's mutilated remains. Daryl finds Carol's scarf and gun, and the five of them move outside, where they reunite with Hershel and Beth. As Rick plans to go back and search for the rest of the survivors, the cries of a baby ring out. Maggie and Carl emerge with the newborn baby. Rick collapses in grief and sorrow when he realizes Lori is not with them, as Glenn consoles Maggie and the others look on in shock and sadness as Rick reels.
- First appearance of Judith Grimes.
- First appearance of Mr. Jacobson.
- Last appearance of Lori Grimes. (Alive)
- Last appearance of Theodore Douglas. (Alive)
- Last appearance of Andrew.
- The title of the episode, "Killer Within", refers to Andrew being the "killer" inside the prison. He released the walkers into the prison, which killed T-Dog and prevented Lori from having a stable C-Section.
- It may also refer to Lori's baby, as it is the main cause of her death, albeit indirectly.
- This was one of the most emotional and difficult episodes to shoot for the cast and crew.
- This episode was referenced in an episode of The Big Bang Theory by Sheldon Cooper. Sheldon asked Leonard Hofstadter if he would like to catch up on The Walking Dead, Sheldon then asked if Leonard had seen "the one where Lori dies", thus spoiling the ending.
- This is the only episode in Season 3 where all of the main cast appear in physical form.
- In this episode, Carol was originally supposed to die, but the producers decided against it.
- When shooting the scene of Rick discovering the demise of Lori, Andrew Lincoln asked Sarah not to be around the set while he is shooting that particular scene. "Andy asked me not to be on set. But I couldn't leave, so I was at base camp with the trailers. I could hear him screaming and crying. I was sitting there with IronE Singleton kind of going, "Oh my God. This is horrible." And then one by one as the scene ended they came back to the trailers to change and go home, and I put my arms around Andy. When he goes down the rabbit hole he goes all the way down. I put my arms around him and I was like, "Look at me. I'm right here. I'm alive! Andy and Sarah are just fine. Rick and Lori are over, but Andy and Sarah are just fine." Sarah said.
- In this episode, there were 24 confirmed walker kills and three living humans. Rick Grimes had the most kills with 6 walkers.
- Lori giving Hershel crutches so he can walk is adapted from a similar scene in Issue 40, where Andrea gives Dale the crutches instead.
- The prison being attacked by walkers is adapted from Issue 34.
- Lori giving birth to Judith is adapted from Issue 39.
- Andrew revealing himself to be responsible for the prison chaos after attacking Rick in the generator room is adapted from a similar scene in Issue 16, where Thomas reveals himself to be the prison killer after attacking Andrea in the laundry room.
- During the scene in which the baby is born, you can see the baby being covered in blood in some shots and clean from any stains in others.
- 'The Walking Dead': Glen Mazzara talks about T-Dog's death and Carol The Walking Dead News (December 17, 2012)
- Kevin Fitzpatrick, ‘The Walking Dead’ Season 3 Comic-to-TV Comparison: “Killer Within”, Screen Crush, (November 4, 2012).