Killer Within

"Killer Within" is the fourth episode of the third season of the postapocalyptic horror television series The Walking Dead. It originally aired on AMC in the United States on November 4, 2012, and was written by Sang Kyu Kim and directed by Guy Ferland. The episode marked Sarah Wayne Callies and IronE Singleton's final appearances as Lori Grimes and Theodore "T-Dog" Douglas and as regular actors on the show. Most television critics positively reviewed the episode, applauding its bleak undertones and the performances, but some commentators criticized the narrative ploys and the direction taken in the program. "Killer Within" was viewed by 9.27 million viewers, including 4.9% of those in the 18 to 49 demographic upon its initial broadcast in the United States. The episode is often cited as one of the show’s best episodes.