Danai Gurira as Michonne in the TV series "The Walking Dead.” (Gene Page/AP)

Warning: This recap contains spoilers.

It doesn’t take long for things to turn bloody in this episode of “The Walking Dead.”

Patrick, who we saw fall ill and die in the season premiere, rises from the shower where he collapsed and wanders into the prison’s cell block D where he bites into a man’s neck like a juicy apple.

Patrick’s feast starts the inevitable walker domino effect, interrupting another idyllic morning for the rest of the prison. Rick and Carl are farming cucumbers together, while Michonne is off on another supply run. Things are always so comfortable and calm when gunshots ring out.

When the fight in cell block D is over, Rick finds one last walker locked in a cell with no bites or injuries. What is obvious to viewers becomes obvious to the group — there is an illness turning humans into walkers.

Hershel imparts his grandfatherly wisdom during an emergency council meeting, advising that anyone exposed should be kept away from others. Whatever the flu-like illness is, no one is sure who might get it or how fast. Even Karen, who has a cough, is sent to quarantine.

As the group deals with the silent threat of a deadly virus inside the camp, walkers outside finally make headway on taking down the prison’s flimsy outer fence. How it’s held up as long as it has already is unclear.

Sasha, Daryl, Glenn and Maggie stab the intruders as the fence bends, and Rick joins them. After having taken a hiatus from taking out walkers, it seems difficult for Rick to do so again. He is now physically standing between his garden and a horde of zombies, caught in limbo. But in the end, he stabs more vehemently and sacrifices his pigs outside of the prison to draw the walkers away. He grimaces at each squealing pig he slices open, but it’s become clear to him that violence is the only way to survive. He even gives Carl his gun back and holsters his own.

In other character development news, Carol’s work to educate the children in “walker safety” is put to the test when she scolds a young girl who cannot bring herself to stab her own father-turned-walker after the attack in cell D. In the end, Carol has to stab him in front of them.

Though the father-stabbing scene is cheesy and a bit over the top, Carol has lived through marital abuse and lost her daughter to walkers. She, like Rick, realizes survival comes with a cost. Her intentions are good.

Finally, with the scary threat of a virus in the midst of the prison, coughing Karen and a fellow prison member are found burnt alive in quarantine. Tyreese, on his way to give flowers to Karen, discovers them. Whatever the illness turning humans into walkers is, it has someone on high alert — high enough to try and snuff it out with gasoline and a match. Hopefully we find out who the culprit is next week.

Romance report: Well. Tyreese and Karen didn’t last long. There was a sweet moment at the beginning of the episode between the two, in which Tyreese croons “I’ve Got You Under My Skin.” Alas, Karen is no more.

Not much to report on Maggie and Glenn. They also share a moment when Glenn snaps a Polaroid photo of her in the morning.

Unanswered questions: Rats. At the beginning of the episode, someone feeds a rat to a walker through the prison’s outer fence. Who is doing that, and why are they trying to bait more walkers to the prison?