Last night’s “The Grove” was without a doubt my favorite episode so far from the second half of The Walking Dead’s fourth season. It’s a good bet that most fans found it shocking, that some found it devastating, and that a few were even enraged that it went where it did. But whether you liked the jarring turn the show took or not, it’s impossible to deny that something actually happened in “The Grove” other than the meandering dialog and action The Walking Dead usually features every week.

“The Grove” finds sisters Lizzie and Mika, Carol, Tyreese and baby Judith, none of whom we’ve seen for a few weeks, heading down the railroad tracks to Terminus like most of the other survivors from the prison. On their way, they find a cabin, and decide to set up camp and rest there for a few nights. After settling in, they begin to discuss whether they should just stay at this comfortable shelter rather than even going to Terminus. But all is not well among these disparate five. Carol is somewhat concerned about Mika, who is still too sensitive; she’s willing to kill walkers, but refuses to kill people under any circumstances, and won’t even shoot a deer when they go out hunting. But Mika is a pillar of stability to Lizzie, who is unraveling by the minute. Lizzie sympathizes with the walkers to an unhealthy degree, and has become increasingly fascinated by them just as she has become increasingly disturbed at the thought of killing them. Mika finds her feeding a mouse to a walker who’s stuck on the tracks at one point. Lizzie seems to think that the walkers are inviting her to join them, that she might even be better off as one of them. But before she can take this thought to fruition, several more walkers come out of the forrest and head right for them. The girls run back to the cabin, where they shoot the walkers down with the help of Carol and Tyreese. This encounter seems like it may have set Lizzie straight, and Carol is able to enjoy her evening with the girls, hoping that things have taken a turn for the better.

But the next day brings those hope crashing down in horrific fashion. After leaving the girls alone to go out hunting, Carol and Tyreese arrive back at the cabin to see that Lizzie has slit Mika’s throat, and was on the verge of doing the same thing to Judith before they got there. Now, Lizzie hopes they’ll finally see the walkers the way she sees them. She threatens them with a gun when they approach, just to make sure they won’t do anything to Mika before she turns. Barely able to even string words together, Carol manages to get Tyreese to go inside with Lizzie and Judith, while she waits alone to take care of Mika, out of sight from the rest of them. Later, when Lizzie is resting, the two adults discuss what to do about her. After some questioning, Tyreese discovers that she was the one at the prison who was feeding rodents to walkers, and who dissected the dead rat they found, apparently for fun. They discuss splitting up, Carol going with Lizzie and Tyreese going with Judith, but they quickly decide that neither of them would make it out on the road without the other. Tyreese gently inquires whether they might still try to save Lizzie, but Carol tells him Judith will never be safe under the same roof as her. Eventually, Carol takes Lizzie outside, walks with her a length away from the house, and tells her to look at the flowers. While Lizzie is looking, she shoots her.

At the end of the episode, Carol reveals to Tyreese that she killed David, and his beloved Karen, back at the prison. She tells him she did it to stop the spread of the infection, and hands him her gun, telling him to do what he has to. Through tears, Tyreese asks if Karen felt any pain. Carol says that she didn’t, that she killed her quickly. Tyreese tells her he understands she did what she thought she had to, and that while he’ll never forget, he can forgive. They continue on to Terminus together.

Anybody who has been watching this season could’ve guessed that the unhinged Lizzie was responsible for what happened to the rats at the prison, but I had forgotten that she had expressed a captivation with walkers early on. So while I knew that Lizzie was unhinged, and probably even violent, I have to say I didn’t see this one coming. I’m not sure if it’s harder to accept that Lizzie killed her own sister, or that Carol was forced to kill Lizzie, but no matter how you look at it, “The Grove” is uncharted territory for The Walking Dead.

Written by showrunner Scott M. Gimple, the question at the center of the episode is whether doing everything you have to in order to survive takes away some of your core humanity. Carol tells Mika that her daughter couldn’t survive because she wasn’t strong enough, but Mika doesn’t want to be strong either. The deer that Mika couldn’t kill, which also appeared after Carol shoots Lizzie, was a symbol of human frailty, suggesting that the more we fight our weaknesses, the more of ourselves we lose in the process.

And Carol, for one, has lost a lot of herself. In “The Grove,” she faces her toughest challenge yet. One more time, she does what she believes she has to in the name of her survival and the survival of the greater group. But this time, it’s too much, and she can’t help but break down in front of Tyreese and confess her past sins.

The whole thing was a pretty great showcase for Melissa McBride. I’m not sure anybody would have put money on Carol being one of the more interesting characters in the beginning, but thanks to a solid performance from McBride and a smartly plotted arc from the show’s writers (one of the few they’ve really managed to nail), she has become if not the most complex character on the show, certainly the most dynamic.

Brighton Sharbino, as Lizzie, does some excellent work here as well. Lizzie has always been fascinating, but as I said before, I wouldn’t have necessarily guessed that she was full-on psychotic. Moments in “The Grove” hint that she may have always been this way, even before the walkers took over, and while I’m not sure I saw enough throughout the rest of the season to suggest that was the case, Sharbino does a compelling job of selling Lizzie’s meltdown within the span of one episode.

While the idea that walkers are still people has been brought up on the show before, most notably in the second season when Hershel and company were keeping them in their barn, having a character become so obsessed with that idea that it takes them over is a new twist, and an interesting one at that. As hard as it was to watch Lizzie go crazy the way she did, it was also kind of understandable. A couple of weeks ago, after watching the episode “Still,” I talked about the gruesome act of constantly destroying human bodies, as the characters on The Walking Dead are continually forced to do. But “The Grove” takes that thought and multiplies it; what would it do to you if you believed these creatures to be more than rotting flesh? If you not only believed their bodies deserved to be treated with respect, but that their minds deserved respect too? Or rather, what would you do if you were the only one that believed they had minds at all? It’s no wonder that line of thinking could drive a person insane.

There were only a few things that really bugged me about “The Grove.” First, I thought Carol and Tyreese’s discussion about what to do with Lizzie was confusing. Carol is the one who initially suggests that they split up, Tyreese with Judith and her with Lizzie. But when Tyreese is willing to go along with it a minute later, she has already changed her mind. It’s hard to accept that she would stay with Tyreese just for survival purposes, because if Carol has proven one thing up to this point, it’s that she can survive just fine on her own. The only conclusion I can come to is that she knew right away she had to shoot Lizzie, and that she just had to work her way to accepting it.

While I don’t have a hard time believing that Carol would kill a child if she had to (to reiterate, she is the consummate survivor out of all of them), I did have somewhat of a hard time believing that Tyreese would forgive her for killing Karen so easily. Perhaps that was just him doing what he had to do to survive too. Maybe he really believed it would be better to live with someone he should by all accounts hate, instead of trying to make it on his own. Maybe after what they had been through together, he felt he understood why Carol did what she did. Maybe his humanity won out, and by some miracle, he really could forgive her. But having watched him obsess over who took Karen away from him this whole season, it still felt like a rapid turnaround, although I suppose I can see why the writers felt it would be more interesting if they kept these two together. Hopefully, everything that happened in “The Grove” will make for some interesting material between them down the road.

Right from the lyrical and mysterious opening shot, “The Grove” stood out as unique episode in The Walking Dead canon. When the second half of this season began, and Judith turned out to be alive, I thought The Walking Dead had once again balked at going all the way. Not that I’m suggesting it’s acceptable to kill two older children in place of killing a baby, it’s just that every time The Walking Dead sets out to prove how dark it can be, to show us how relentlessly hopeless its world is, they usually pull back too soon into their typical mode of cheap thrills and excessive gore. But the buckets of blood the show usually uses to satiate its violence-hungry viewers could never be as unsettling as the events of “The Grove.” It was an extreme episode, absolutely, but their attempt to jump from physical horror to psychological worked. Usually, when the show does this, it hurriedly goes back to stretching itself thin again; more of the same wandering around, more of the same stilted conversations, more of the same several zombie kills per episode average, all while we wait for another truly brilliant episode. No, I’m not sure that “The Grove” will send The Walking Dead in a new and better direction, I’m just sure that for what it was, this episode was excellent.