After discovering the bodies of Karen and David, Tyreese flips his wig and hulks out on Daryl and Rick, the latter of whom hulks right back while Carol watches in horror. In the stressful aftermath, Sasha comes down sick and goes looking for Dr. S. in D Block, which has become a consumption ward where every victim seems doomed to eventually start consuming each other.
While more people get sick and more patients (including Glenn) are put in isolation in A block, Hershel dispatches a mission to a veterinary college fifty miles away to find antibiotics. Daryl asks Tyreese to join him, Michonne, and Bob on the trip, but Tyreese is still on his justice crusade and doesn't sign on until after a chat with his sick sister.
Meanwhile, Hershel decides to go on a mission of his own, out to the woods to collect elderberries, and Carl insists on going with him for protection. And wearing his stupid-ass hat again, too, which comes in handy for their encounter with the two least threatening zombies ever. When Hershel returns to the prison to deliver the natural remedy to the patients, Maggie and Rick try to talk him out of it, but he's undeterred and he's got a whole speech to back himself up with. And then, in the sick-block, Hershel bucks up Glenn and catches a faceful of blood coughed into his face by Dr. S.
Carol, who has been trying to be a rock for everyone, loses it after having to send Lizzie into quarantine and being asked by Tyreese to check on Sasha, and spills most of the prison's already-low water supply. And then Rick has to go rescue her while she's outside the fence trying to clear the intake hose in the creek and nearly gets overrun.
While on the road, Daryl seems to almost pick up a live broadcast on the car radio and, while distracted, ends up driving right into a massive herd. The away team has to abandon the car and flee into the woods, briefly leaving behind a slow-moving Tyreese who takes his time working his way up to hacking down zombies with his framing hammer, but eventually catches up. Still, the chances of them coming back with the needed medical supplies aren't looking too good now that they're on the run, and on foot.
And finally, after conducting a brief investigation into the killing of Karen and David, Rick confronts -- and gets a confession from -- his prime suspect: Carol. Aw, maaan.
Glenn is waist-deep in a fresh grave, wearing gloves but with his bandanna hanging loosely around his neck, because it's not like any of their lame hazmat measures are accomplishing anything anyway. He pauses to look over at some other nearby grave markers, including one with Patrick's glasses hanging from it. He shares a glance with Maggie, who is digging another grave nearby, and then we see that two other people are digging while a third stands around. Don't wear yourself out, third person.
Inside the prison, Hershel watches as Dr. S listens to the last heartbeats of a patient who has already lost most of an arm, then leaves him to it while Dr. S pulls out his knife to perform what passes for last rites these days.
Tyreese has brought Rick, Daryl, and Carol to A Block's tiny exercise yard, where the two charred corpses still lie smoking on the concrete. Tyreese explains, "Somebody dragged them out here and set them on fire! They killed them and set them on fire!" Look who's all CSI: Backwoods Georgia all of a sudden. Tyreese angrily turns on Rick, demanding that, as a cop, Rick needs to find the killer and bring them to Tyreese. Daryl tries to pull Tyreese back and Rick tells Tyreese he gets it. "I've been there," he says, "You saw me there, it's dangerous." It's not about you this time, Rick.
Tyreese stays right up in Rick's face, and when Daryl tries to take Tyreese's arm, Tyreese grabs him and pins him against the grate on the far side of the yard. Even while being manhandled by a much larger dude, Daryl maintains the presence of mind to hold out his hands to Carol and Rick to show that he's got this. Daryl and Rick both continue trying to calm Tyreese down, but Tyreese just ends up decking Rick, and then punching him again while he's down. Carol screams at Tyreese to stop, and now Daryl's done being calm, hauling Tyreese off of Rick. But Rick's berserker rage has been reawakened and he somehow beats the shit out of Tyreese before Daryl pulls Rick off of him. Carol stands there with her hands over her mouth, and Rick looks miserably at his bloodied hand and his bloodied friend on the ground. Okay, good meeting!
After the credits, Rick is back in the prison as Hershel patches up his battered right hand, which Hershel says will be sprained for at least a week. "I wouldn't plan on much typing the next few days," he advises. Good one. But he's still concerned about Rick, and how the bad found its way in after all their efforts to keep it out. "No, it's always there," Rick says, glancing at his gun behind him. Hershel tells Rick there will be a council meeting tomorrow, as though to invite him. "We just lost twelve of our own. Two more killed in cold blood." Rick thinks he's done enough damage, and Hershel tells him that when he fell off the wagon, he got back up because he had shit to do. In other words, Rick, stop feeling sorry for yourself over your addiction to violence, 'kay?