Alan wakes up in his quarters and does a lot of hungover blinking. He has blood on his hands. He flashes back to throttling Sarah and some bloody utensils …
… and we flash back to 1601, where Michael stares hungrily at a woman threshing a field. Mlle. Durant explains in voice-over that Michael married the woman, though "her heart belonged to another," and she bore the other man's son while random passersby mocked Michael as a cuckold. Michael vowed never to feel such pain again and burned down his barn with her in it while muttering in French.
Jules isn't seeing how "this murderer" can help them bring down Ilaria. Durant explains that Michael has perfected infertility among mortal men; Ilaria can control the world population this way, instead of via genocide. Involuntary sterilization doesn't sound like the greatest deal either, but Jules agrees that it's the better option.
Meanwhile, Michael is in a snit because he can't find his budding knife. He barely listens to Amy's report on the hunt for the infected, namely that they've only found four out of eighty-three. Michael puts Amy in charge of organizing the lab and falls for her obvious crap-stirring when she mentions that "people are talking about leaving the island."
Peter has a new cellmate: Anne, who explains she's been framed. She quavers that she's sure Michael will realize his mistake any moment now. Peter's like, riiiight ... good luck with that.
Alan wanders into the quarantine area where Kyle tells him he looks like hell and wonders where he was "all night." The search was a bust, he adds; Olivia and her crew are better at hiding the infected than they thought. (Better, but not great, because as Kyle's saying that, an infected Killigan's Islander is menacing Olivia.) Alan surveys the four patients that did get found and observes that the sedative's wearing off, then asks if Kyle's seen Sarah. Kyle thought she was with Alan. Alan's cagey but Kyle doesn't notice and offers to accompany Alan to the lab to look for her.
Before they can head out, the abbeyites gather in the dining hall as Michael requested so he can take the podium and calm them down. The announcement that the dining hall is the safest place on the grounds at the moment, and that nobody is to leave until further notice, has the opposite effect, as the crowd peas-and-carrotses about getting separated from family and leaving the ill to die. He's losing the room, and as Amy makes a triumphant duckface, an abbeyite wings Michael in the shoulder with some food. He's furious but settles for ordering Landry to post guards.
The lab is empty but for broken glass and one of Sarah's boots. Alan picks up the boot and flashes back to Sarah on a lab table, and blood; he's visibly shaken, but thinks he knows where Sarah is -- in an outbuilding he's "almost" visited. "I came to this island for a reason," he tells Kyle, and it's buried under the abbey. Kyle frowns but follows him.
Sarah is on a gurney, covered with a sheet that's bloody near her groin. She sits up with a gasp, flashing back to what seems like an abortion of the Immortaletus.
Michael's muttering to The Wall O' Matriarchs about the devastation of orchards. Amy comes in and snottily asks who he's talking to, then reports that Landry had the food-chucker taken to a "contemplation cell." Michael overrules that order, and when Amy pouts that the guy "transgressed" and should be punished, Michael reminds her who's in charge by, among other things, choking her. Unfortunately for those of us who find Amy super-irritating, he releases her and she runs off.
As Sarah makes her escape -- and steps on a human tooth with her one bare foot -- Anne tries to apologize to Peter for how "our fellowship" has treated the CDCers. He is not having one bit of that, but when he yells at her, Anne snaps and yells back -- she's sick of being taken for granted! Peter has no idea what it's like! Oh, but he does, and they bond over how much working with family sucks before Amy appears at the grate; Michael's losing his marbles. Anne's like, Michael doesn't always make sense, but you have to protect him now, and when Peter suggests talking about it "up top" instead, Anne smugs that she's not leaving until Michael releases her. Peter, hilariously: "Are you kidding me?" Anne tells Amy to go "offer" herself to Michael; Amy brats that she doesn't have to listen to Anne, or Michael, or Peter for that matter, and stomps off. Peter's like, nice one, Mom.
In the abbey catacombs, Sarah is guiltily "borrowing" a pair of boots from a corpse when she hears banging and screaming. Doubled over in pain, she scuttles away … and stumbles into a domestic-violence situation with an infected abbeyite and his terrified kids. The dude's using a meat cleaver to break down the door Sarah and the kids are deadbolted behind but stops for some reason, and Sarah lets the kids talk her into taking them with her.
They creep away, just missing Kyle and Alan, who's explaining that the virus isn't doing a good job spreading its DNA because it kills its hosts too quickly. His theory: the virus was augmented by humans. After Kyle shoots a padlock, they gain entry to the place Alan couldn't get into before and find the gurney Sarah was on, next to a tray of bloody instruments. Alan flashes back again to whatever procedure Sarah underwent, but he can't fully envision or describe it. Kyle's starting to freak out and Alan informing him Ilaria's responsible for Narvik doesn't help; neither does seeing that Alan's exhibiting the same eye movements and memory loss as the children who stoned Kyle. Alan agrees he was probably drugged. Realizing he may have delivered Sarah to her fate, he sadly suggests splitting up to find her. Kyle doesn't think that's a good idea. Neither does Alan, but he's "all out of good ideas."
Peter has a good idea: convince Anne to team up with him and speak truth to (Michael's) power. Elsewhere, Kyle is getting spritzed by the misters in the botany lab. He runs to hide, then spies as Michael comes in, puts a mournful polka record on the gramophone and muddles the flowers of a purple plant. Lurking in the stacks, Kyle finds the abbey's journals from the 1600s, including the family trees.
Sarah jollies the little boy out of his fear with a story about the Congo and Superman; naturally, pantsing around with Story Hour lets Cleaver Dad catch up to them. Sarah can't run far thanks to the abdominal pains, the kids are frozen in terror, and Cleaver Dad and the banana pudding that's leaking out of his mouth are about to attack when Alan appears and subdues him. …Wait: he collapses before Alan can inject him. That means the disease is speeding up in how fast it kills people, information Sarah and Alan have no problem clinically analyzing while Cleaver Dad's now-orphaned children are standing right there, staring at their dying father. Finally Sarah mentions it and Alan gently offers to bring them to the dining hall, but Sarah needs to go to the infirmary and use the ultrasound.
Amy slams into Michael's lab to inform him that her path doesn't lead to his bed. He seems to admire her defiance but says he knows all about her schemes with Landry and the honey. Her "Machiavellian" approach will serve him well, because it's time to thin the abbey herd -- using the opiate poison he's got bubbling on the Bunsen burner. Amy's horrified; she's even more horrified when he notes that, after other community purges, her ancestors/sisters (… "ansisters"?) bore him as many as 22 kids -- and she's expected to do the same. She tries to refuse but Michael chuckles that she's doing it, "with or without [her] teeth," then locks Amy in a case with the poisonous plants. Eventually she'll understand and give in, he tells her, adding that of all his daughters -- sing it with us if you know the words -- she's always been his favorite.
Alan gives Sarah an ultrasound. He tries to rationalize why there's no baby on the monitor, but there's no baby because there's…no baby. Sarah doesn't remember much from last night, just a lot of blood. Alan gathers his courage and admits that he "lost time"; he might have attacked her himself. Sarah wonders, sobbing, if Immortals disgust him "that much," and accuses him of never wanting the baby. He protests that he had no idea what he was doing, but she orders him out.
Amy begs Kyle to let her out. He's like, hmm … nope! But she says she can tell him where Sarah is. Kyle's like, nope again, and leaves her there to go look for Sarah himself. He comes upon the oubliette as Peter's about to hoist Anne up to the grate, and gives Peter the sitrep as he's hunting around for a rope -- including the solution Michael made from the purple flowers. Anne hears that and slumps to the floor: it's "a thinning." Kyle doesn't get it, so Peter name-checks Jonestown and Heaven's Gate: "They're all going to kill themselves." Not sure that's an affirmative choice, but: yep.
Michael announces that the CDC has come up with an antidote as helpers enter with trays of the "oral vaccine." He sends Landry and his men to the perimeter and proves the vaccine is safe by swigging a cup himself. The Killigan's Islanders drink the serum as Peter, Kyle and Anne sprint towards the dining hall. The little boy Sarah protected spills his, then looks on in confusion as the other abbeyites start choking and flailing. Anne and the CDCers pound on the bolted door and beg Michael to stop as Michael regards his dying flock with his usual creepy smile … and gives the kid a fresh cup of poison, which the kid drinks. Shudder.