Things are finally heating up in Clone-ville. After three episodes of hearing Susan's name, episode four brings us face to face with the character again in a hospital bed. P.T. Westmorland saved her life — but why? He turned her daughter against her and is responsible for this whole mess, but he says he still needs her, so here we are.
We're also at Revival, where Charlotte and Aisha notice one of the pigs in missing. They go out looking for her in the woods — bad idea. They hear squealing and spot the pig, bloody and surrounded by food and what looks like a human tooth. Mud stumbles upon the children and ushers them back to camp.
Sarah once again tries to connect with Kira, who's truly having none of it, although she does reveal that Rachel clipped her fingernails, took some blood, and chit-chatted with her. When Sarah goes in for hug, however, Kira cries out in pain. Upon taking off her sleeve, we see Kira has a cut on her arm...which probably has something to do with the knife she was holding at the end of the last episode. Sarah, of course, blames Rachel, and brings Kira down to show Felix and Mrs. S.
"It was me," Kira reveals. "I cut myself. Stop blaming Rachel." She wanted to see how fast her injuries would heal. Mrs. S sends Kira off with Felix, and tells Rachel to stick with her — she has a lead for helping Kira.
There's some uncomfortable dirty talk between Susan and Westmorland before Ira, a Castor clone, interrupts them. He and Susan have a sentimental reunion before we jump back over to Sarah and Mrs. S.
Scott has been gathering research on P.T. Westmorland, including finding old books and putting together his life story. However, for the past 100 years he's been assumed dead, and they're looking for any hint of his activity. Sarah and Mrs. S leave to go "get a drink," which turns out to be a ruse to spy on a person named Elizabeth Perkins. Mrs. S believes that, somehow, Perkins has the key to P.T. Westmorland — they just need to get her ID. Seamlessly, they pull off a fake argument that distracts Perkins and allows Sarah to grab her wallet. Mrs S, however, says behind to drink.
Taking a closer look at the ID reveals that her full name is Dr. Elizabeth Perkins, a professor in the department of psychology at Amherst Medical College. Sarah, pocketing the ID, returns the wallet to Perkins' table just in time, and she and Mrs. S make their escape unscathed.
Back in the car, Mrs. S explains that they're going to impersonate Perkins to get into a facility called Cedar Ridge and talk to a defected neolutionist who is likely being held there against their will.
"Who's feeding you info close to P.T.?" Sarah asks, but receives no answer. She decides to make a quick stop at a convent — which makes sense when you remember that's where we last saw Helena.
At Revival, Charlotte shows Cosima the tooth that she found in the woods. Cosima takes a closer look and confirms it's a human tooth, which inspires her to confront Mud and find out what's actually out there.
"It's not his fault," Mud says ominously, but won't say more in fear of getting in trouble.
Susan and Ira catch up, when she explains her history with P.T. Westmorland. They share the same vision, she says. Their feud is just about the means.
At the convent, Sarah reunites with Helena, who's been writing her memories. Sarah opens up about her struggles with Kira, and Helena says that Sarah should tell her daughter the truth about the clones.
Over with Felix, who has a sleeping Kira in his apartment, there's a surprise visitor. Adele, his biological half-sister, has arrived, and she knows everything. Well, not everything, but she knows about the clones and Kira. Adele has her own secrets: she's an embezzler, and they have to go to Switzerland to do a project for Mrs. S.
Cosima spots Mud out at night and secretly follows her into P.T. Westmorland's house. She's helping hook him up to a machine. Cosima sneaks past them and into a basement.
Mrs. S and Sarah, who are now dressed as Perkins and her assistant, respectively, arrive at the hospital. They put on a bit of a show — her assistant messed up! They were supposed to meet someone! Ack! Oh no! — and win over the favor of the receptionist, who says he'll sign them in.
They go looking for the defected neolutionist, who turns out to be Virginia Coady, the military advisor from season 3 who put Helena through so much trauma, secretly infected women with the Castor disease, and killed Paul. They use adrenaline to bring her out of her dizzy state and ask her about P.T. Westmorland.
"Get me out," she says "Then we'll talk."
"You want to get out here?" Mrs. S replies. "You need to earn it."
This is where things gets crazy. She reveals that Susan Duncan put her in the facility, that she first worked with P.T. Westmorland on his first human subject, that it was a child with a unique genome that they couldn't unlock. He got sick, and grew tumors, but they kept pushing. They created a monster — the very monster who lives in the woods.
As Coady explains these details, we watch Cosima see where the subject is kept in the basement of P.T.'s house, we watch her follow Mud into the woods to feed the subject-turned-creature a sacrifice.
After things got bad, Coady explains, Duncan couldn't forgive her. Coady took Castor and Duncan took Leda, with Westmorland working to keep the two apart. Coady says she won't give them more information, however, until the help her escape, but before they can, Dr. Nimitz — the doctor they said they were supposed to be meeting — arrives. He tries to take them away, but Coady leaps on Sarah and steals her keycard, causing a diversion.
Sarah and Mrs. S escape. They reunite with Felix and Adele to talk about Switzerland and convince Felix to follow his sister to Europe.
Susan Duncan tells Westmorland that Rachel is too damaged for the responsibility she's been given, and that he's lost without her when it comes to the science. She'll only join him if she's given access to all of Rachel's data on Kira. Westmorland agrees, promising no more secrets, but emphasizes that Rachel still has the reigns. They toast to the future.