'Better Angels' (Season 2, Episode 12)
Though it's just the penultimate episode of Season Two, "Better Angels" brings to a head everything that the show's sophomore go-round has been about, culminating in the scene where Rick (Andrew Lincoln) finally kills the fully deranged Shane (Jon Bernthal) — and where Carl (Chandler Riggs) kills him again, when Shane comes back as a zombie. But what makes this episode great isn't that it contains the most significant death that the show had allowed up to that point, but that it comes just as Rick's group was had finally found sanctuary. The noise of Shane's death attracts a fresh horde of walkers, who will drive everyone away from the farm they'd settled in by end of the season finale. Meanwhile, Rick reveals a secret he learned at the end of Season One: that everyone who dies becomes a zombie, regardless of whether they've been bitten or not. Once again, The Walking Dead manages to pull hopelessness out of hope, while forcing its heroes out into the wilderness to try again.