Paul digs and finds the ugly truth behind the Castor Boys’ logbooks of names, pushing him into action. Meanwhile, Felix is desperate for info on Sarah’s whereabouts, and presses the still-ailing Rachel for any shred of a lead. In order for Donnie and Alison to take their money-making endeavor to the “next level” she must introduce Jason Kellerman to her unique business plan.
Sarah wakes up, and walks to the middle of the complex. She hears Kira giggling, and she runs to meet her. She follows Kira into fort-like structure, and sees herself on a cot receiving blood from Rudy. After he licks her hand, Sarah realizes that she is dreaming, actually wakes, and vomits. Sarah knows she was hallucinating, but she has a Band-aid from where she received blood.
Kira is skyping with Mrs. S and Felix from Iceland, where she is staying with Cal. The conversation seems to be going well until Kira asks if Sarah is mad at her. Mrs. S and Felix assure her that this is not the case, and they end the call. After they hang up, it becomes clear that Felix is agitated that S has not been able to locate Sarah more quickly. Gracie, who has been staying with Mrs. S, enters with tea and attempts to serve her hosts.
Cosima wakes in Shay's apartment to the sound of her phone vibrating. Shay asks about Sarah, and says that Cosima said Sarah's name in her sleep, so she assumed that she was an ex-girlfriend. Cosima explains that Sarah is like her sister, and a wilder version of herself.
In celebration of their newfound wealth, Alison and Donnie twerk on their bed in stacks of money. This continues until they are interrupted by Gemma. Alison and Donnie proceed in getting ready for their day, and they discuss their later drug deal with Jason.
Cosima arrives to DYAD to meet an irritated Scott. She enters the lab to find none other than Delphine waiting for her. They are arguing about Sarah's disappearance, and Delphine mentions both the Castor brain and Gracie. Delphine points out that the misfolded protein found in Seth's brain was also in Gracie's DNA, and decides that Gracie will come in for a follow-up.
Paul returns to the Castor complex to find Sarah shivering and sweating on a cot. Sarah asks for Paul to help her escape. When he refuses, she tells him that he is the worst out of everyone because she does not know whose side he is on. Virginia Coady enters, and claims that Sarah is reacting to an anti-inflammatory she gave her. Sarah asks if Helena escaped, and Coady replies that she did, but she will either die, or Rudy will find her.
Helena is seen running through the desert, and she falls. Pupok taunts her, saying that she regrets leaving Sarah. Helena replies that she regrets nothing, and proceeds to eat Pupok.
Paul sits down at a table where Dr. Silva is eating. He claims not to know what Coady did to Sarah, but Paul eventually gets him to confess. He tells Paul that Rudy brought a sick girl to camp six months ago, and she was treated onsite. Following that incident, the science became more secretive. He tells Paul to go to her quarters to find more information.
Delphine and Cosima are standing in front of an elevator waiting for Gracie, and Delphine asks Cosima if she is feeling well. Their conversation is interrupted by Felix and Gracie's arrival. They lead Gracie into the lab, where they enter without Scott and Felix. Felix asks Scott to take him to Rachel, so that he can obtain more information concerning Sarah's whereabouts and Castor. Scott initially claims he does not know where Rachel is, but he agrees to take Felix to Rachel.
At the Castor camp, Paul approaches Mark. They talk about the fact that Mark brought Sarah into the camp, and about Mark's relationship with Gracie. Paul asks Mark to do something for him, off the record.
Alison is with Jason, and she pays him for the prescription pills. Alison begins to tell him that she and Donnie would like to continue in the drug business when he pulls up in a new car. Jason says that they would need a front in order to be more active in the drug business.
Mark meets Paul outside with a set of keys, and tells Paul that they have five minutes. Paul enters Coady's room. Meanwhile, Cosima is giving Gracie an exam and informing her of the protein that they found in Mark's brother, Seth and herself. Mark and Paul are going through Coady's files and discovering similar information: that the Castor clones' sickness is sexually transmitted.
Upon learning this information, Paul and Mark go to the room where Sarah is being kept and place Coady and Styles under arrest. He now knows that she is attempting to use the Castor disease as a biological weapon to sterilize women. It is revealed that Coady gave Sarah Rudy's blood in order to see the effects of the Castor pathogen on her body. Sarah begins hallucinating that Charlotte is next to her bed. Charlotte tells Sarah to come with her. Sarah follows Charlotte into a tunnel.
Sarah and Charlotte can hear and see Beth's home tapes. Sarah runs into a house, and sees Beth making tea at the kitchen sink. Beth tells Sarah that she was thinking about the day Paul moved in with her. Beth takes a few pills, and her demeanor changes. She accuses Paul and Sarah of being liars, and Sarah's response is that she did not know Beth when she took over her life. Sarah tells Beth that she is trying to help her sisters, but she keeps failing. She reveals that she feels that she allowed Beth to commit suicide, but Beth says that it was her own decision. Sarah tells Beth that she only took over her life to benefit Kira, to which Beth replies, "we do terrible things for the people we love. Stop asking why. Start asking who, sister." Beth then turns and walks away, with the footage from her suicide playing parallel. Sarah immediately wakes up and asks for Paul, who is talking to the unnamed man from the bench about deposing Coady.
Rachel is in her room painting water-color symbols. She turns to see Felix, but she is unable to say his name. Felix asks about Castor, and Rachel says that they are only rumors. Felix tells her that they are real, and that they have taken Sarah. Frustrated with her passiveness, he paints on her eyepatch, taunts her, screams in her face that no one cares about her. Rachel cries, and asks for Felix to get her out of DYAD. Scott notices that the symbols she painted matched those in Duncan's copy of The Island of Dr. Moreau, and he takes the painting.
Donnie and Alison are sitting in their car outside of Bubbles, Alison's mother's shop. Jason meets them there. The three enter with Jason, and they show him around in an attempt to convince them to allow them to use it as a drug front.
Back at DYAD, Gracie's visit is ending. She asks Cosima if she is a monster for not wanting children, and Cosima tells her that she is not. When Gracie and Felix leave, Delphine tells Cosima that she misses her, but Cosima leaves without responding.
Rudy gets a call that there is a situation at base.
Delphine is sitting in an office drinking and looking at photos and videos of Shay and Cosima.
Cosima arrives at Shay's apartment with the intent of slowing their relationship down, but they start kissing instead. She gets a call from Scott, and he tells her that Rachel knows that code in her father's book.
At the Castor camp, Sarah and Paul are talking about the Castor disease. Sarah asks Paul if he loved Beth, and he only says that he will always carry the weight of Beth's suicide with him.
Sarah and Paul confront Coady about giving her Rudy's blood. She does not seem alarmed, only amazed that Sarah is exhibiting no signs of sickness. She tells Sarah that she knew Sarah would survive it because she is immune to the Leda disorder, and Castor and Leda's disease is the same; it just attacks different parts of the body. Coady says that her aim is isolate the pathogen and develop it into a biological weapon for warfare.
Rudy arrives back to camp, and immediately kills a guard. He releases his brother, Styles. Meanwhile, Sarah and Paul meet up with Mark. Paul calls the unnamed man from Arlington, and learns that he is double-crossing him. He tells Mark to return to his quarters, and leaves with Sarah. While attempting to escape, they encounter Styles, who Paul kills, but not before he is stabbed. Paul leads Sarah to a tunnel, and locks the gate, and tells her to leave without him. As he leaves, he turns to her and says, "it was never Beth I loved."
Sarah waits at the gate, and Beth and Paul's home videos play again. Coady and Rudy are out of confinement, and they go to the room where the science is being held. Paul is waiting for them, and he asks Coady to cure the boys, and discontinue the warfare research. Sarah finally decides to leave the gate, and moments later, Coady shoots Paul. Paul drops a grenade, which destroys the remaining science and ends his life. Footage of Charlotte, Beth's videos, and Kira plays prior to Helena dropping into the tunnel to rescue Sarah. They leave together.
Once again, Rachel is painting the symbols. This time, she is looking at a childhood picture of herself and Ethan, and she is crying.