High Quality Content by WIKIPEDIA articles! "Killer Within" is the fourth episode of the third season of the post-apocalyptic horror television series The Walking Dead. It originally aired on AMC in the United States on November 4, 2012. In this episode, walkers invade the vulnerable prison, which has been sabotaged by a person within the complex. During the ensuing chaos, Lori Grimes (Sarah Wayne Callies) goes into labor. Meanwhile, Michonne (Danai Gurira) and Andrea (Laurie Holden) have a disagreement on whether or not they should stay in Woodbury and trust The Governor (David Morrissey).