Krystal's roommate and vlog partner Brie ends up losing some of her hair, and Krystal becomes convinced that "Big Cosmetics" has poisoned Brie. She turns to Scott and Art for help.
Mr. Frontenac appears to pick up Kira, but Kira explains that she's been sick and vomiting. Frontenac is hesitant to leave without her, but Kira pukes right on his shoes. He leaves, telling Rachel that Kira was too sick to come to meet with her that day. As it turns out, S and Sarah made Kira sick on purpose (with her permission) so that Kira wouldn't have to go, because of Delphine's warning to S. S tells Sarah that she has more than one source on the island, but does not tell her who the second source is.
Cosima remains trapped in Westmoreland's basement. Mud, wearing a cowbell as punishment, brings her food. Cosima tries to recruit Mud to help her, but Mud resists and refuses to let her out.
Krystal tells the group that a man she was cultivating as a source (Len, the head of Blue Zone Cosmetics) ghosted her. Sarah and S find that Len sold the company to Dyad Institute. They wonder why Dyad is interested in a cosmetics company. Sarah decides to go undercover as Krystal to meet with Len and find out.
Instead, Krystal has Brie distract Scott and sneaks away once Art and Sarah leave to intercept Len. Krystal meets with Len herself, making out with him and inelegantly getting information from him, as Art and Sarah listen in and watch via Krystal's surveillance equipment. Meanwhile, Brie confesses to Scott that she stole cream from Len's company, which he realizes is what made her sick and caused some of her hair to fall out.
While Krystal is in the bathroom, Len finds the cream Brie stole. Krystal attacks him and takes him down after he calls her stupid, demanding to know what's in the cream. It turns out it was an experimental prototype — a dermal delivery system for regenerative therapy. Sarah and Art realize that Dyad could put anything in that for experimenting.
On the island, the villagers are getting more and more restless after the death of the man Yannis killed before Westmoreland killed him. Aisha also dies, after Westmoreland's experimenting on her. These deaths rock Mud's faith in him.
After Westmoreland brings in Virginia Coady to help, Susan turns against him. She, Ira, and Cosima plot to escape the island, take a stand against everything, and take Westmoreland down. Ira discovers that Westmoreland's treatments are parabiosis — he is taking the blood of the children and transfusing it into himself.
Westmoreland calls Rachel and insists that she begin Kira's hormone therapy so they can start on their surrogate experiment. Rachel agrees and she goes to the house to retrieve Kira. Mrs. S reluctantly gives Kira up.
With cooperation from Mud, Susan attempts to poison Westmoreland. But when Westmoreland is kind to her, Mud (who previously revealed that she was a junkie who OD'd and was saved by the old man) turns on Susan and informs Virginia, who saves Westmoreland. In retaliation, they kill Susan by hooking her up to the same IV she was attempting to use on Westmoreland.
Ira lets Cosima out of her captivity. She realizes that Ira is glitching. Cosima tells the angry villagers the truth about Westmoreland, inciting insurrection in them. They begin burning the village as Cosima escapes with Charlotte and the cure by boat. They wait a bit for Ira and Susan, but leave when it becomes clear they are not coming. Ira, whose nose is bleeding, finds Susan dead and bows his head to her lap, staying with her.
Westmoreland looks out over his burning community, as Mud looks down and finds the photo of a young Westmoreland with young Susan, revealing that the entire legend about him being a 170-year-old Westmoreland is completely a lie.