Sarah, Felix and Mrs. S take a trip with the hopes of tracking down the Castor Original. But they are not alone. Back home, Donnie tries to save the family business when Jason throws the Hendrixes under the bus, but it is Helena who manages to secure a “refund.” Meanwhile, Cosima becomes suspicious of Shay, and Delphine takes the matter into her own hands. But nothing will ever be the same again when Leda finally finds what they’ve been looking for.
This episode contains examples of:
- Berserk Button:
- Never threaten kids in front of Helena, especially ones she's related to.
- Delphine's cold anger toward Shay shows that one should think twice before doing anything to harm Cosima. Subverted in that Shay was not the mole.
- Bullying a Dragon: Threatening Donnie's kids was not wise to do. Especially since they had no idea which Leda clone they were dealing with...
- The Bus Came Back: Ferdinand returns after his appearance in the Season 3 premiere.
- Call-Back: The jacket Helena wears when she breaks up Pouchy's operation is the same one Alison wore when she let Aynsley die
. - Chekhov's Gun: The paper cutting blade. See Hoist by His Own Petard.
- Curb-Stomp Battle: By all indications, Pouchy and crew were no match for Helena. She emerges covered in blood, but with no apparent injuries.
- A Day in the Limelight: Mrs. S. She takes Sarah and Felix to London to track down the Castor original, reunites with the old gang, and belts out a tune in the pub.
- Dissonant Serenity: A bloody Helena walks out of the slaughter of Pouchy and associates, hands Donnie a bag full of money, and deadpans "I got refund. We should leave now."
- Finding Judas: Gracie turns out to be the Castor mole inside Leda, but she's only doing it because she wanted to reunite with Mark and save him from the Castor pathogen before it kills him. She even calls Cosima and tells her that she's sorry.
- Gory Discretion Shot: We don't see what Helena does to Pouchy and family, but judging by how bloody she is afterward (despite no apparent injuries), it wasn't pretty.
- Hoist by His Own Petard: Pouchy's weapon of choice to intimidate people is the blade on a big-ass paper cutter. Guess what Helena slaughters him and his gang with?
- Implied Death Threat: During her interrogation, Delphine tells Shay a story about a girl she knew from boarding school who attempted suicide by slitting her wrists in the bathtub. While she's telling this story, she runs bathwater.
- Make It Look Like an Accident: Delphine threatens Shay with this when she thinks that Shay is a mole working for Project Castor.
- Matricide: Siobhan comes close to killing her mother so no one can get more Castor DNA, but Sarah talks her down, saying that they need Kendall for Leda DNA too.
- The Mole: Its revealed that Gracie is the one who told the Castor folks about Duncan's book because they promised to reunite her with Mark.
- Mood Whiplash: The Helena subplot begins with her happily making soap in the Hendrixes' garage while dancing and lipsynching to the Turtles' "You Baby" - and ends with her bloodily wiping out Pouchy's gang.
- Mugging the Monster: Pouchy's family could intimidate Donnie easily enough, but not Helena.
- Offscreen Moment of Awesome: Helena's dispatch of the drug dealers.
- Paper-Thin Disguise: To impersonate Alison, Helena covers up her hair and passes her accent off as the bad kind of cold that messes with your syntax.
- Parental Sexuality Squick: Averted, Sarah and Felix all but high-five Siobhan when they hear she hooked up with Carlton, to her mild embarrassment.
- Pay Evil unto Evil: Helena turns Pouchy's paper cutter against him when his niece threatens Donnie's kids.
- Red Herring Mole: Cosima and Delphine believed that Shay was a spy for Castor, but it turns out that she isn't.
- The Reveal: Sarah finally tracks down and meets the Castor original: Kendall Malone, a genetic chimera who absorbed her male twin in the womb and has two cell lines present in her blood. This means that she's also the Leda original as well. But that's not all. Kendall Malone is also the biological mother of Mrs. S, meaning that, in a sense, Sarah's her own grandmother.
- Soundtrack Dissonance: The scene of Mrs. S singing in the bar is interspersed with scenes of her friend and contact, Terry, being beaten to death by Bulldog, Ferdinand's lackey.
- Twin Switch: Helena plays Alison, as mentioned in Paper-Thin Disguise.
- Wait Here: Donnie asks Helena to wait in the car while he returns the pills to Pouchy. As Sarah could have told him, that trick NEVER works.
