'The Grove' (Season 4, Episode 14)
Midway through The Walking Dead's fourth season, the prison was finally overrun with walkers, and Rick and company scattered in a panic, losing track of each other. For the rest of the season, the show told smaller stories about the characters off on their own — resulting in some of the show's most memorable episodes. The series has never been bleaker — or more moving — than it was "The Grove," in which Tyreese (Chad L. Coleman) and Carol (Melissa McBride) find a relatively secure house in the country. Peace and stability seems to be at hand, until one of the children they've been looking after, Lizzie (Brighton Sharbino), becomes convinced that it would be better for everyone if they just died and were reanimated as zombies. Then Lizzie murders her own little sister, and Carol realizes what the humane thing is to do, in a scene that eerily echoes Of Mice and Men.