Sarah pursues the missing Helena who is held in a faraway compound. Sarah must use her wiles - and acting chops - to deter a Topside investigator who threatens the Leda sisters' lives. Meanwhile, Cosima appears to be rebounding from her illness, while Alison and Donnie face newfound financial woes. But when the menace of Castor rears its head once more, Sarah and her entire family must come together to survive. Written by Amanda

Castor pursues the Leda clones for original tissue samples. Helena, who is pregnant and imprisoned, is examined by a mysterious new villain. The Castor boys are also out to play, toying with a frightened young woman, Patty, in a sexy switcheroo that ultimately sets Sarah - and Art - hot on the Castor trail. But it's not all fun and games for the Castor boys, as Sarah gleans they may have a mysterious defect that puts their lives in peril. Written by A

Leda and Castor are both on the hunt for original clone DNA. On-the-lam, Mark and Gracie pursue new leads to find the samples that might set them free, while Art and Sarah reunite to track them down. Meanwhile, Cosima and Scott try to learn more about Castor's biology and Alison's new money-making venture is going gangbusters. A shocking revelation about the Castor-Leda connection leaves the sisters reeling, just before Sarah witnesses a deadly Prolethean-Castor face-off. Written by Amanda

Bonnie has shot Mark and has left him for dead. Sarah is able to find and help him, doing so because she knows that the Castor clones are the Leda clones siblings, and that Mark seemingly is trying to get away from the project. In helping Mark, Sarah hopes to get some information from him about the Castor headquarters and Helena's situation. Also finding out from Mark about the tissue samples that Henrik stole, Sarah wants to find the box that Mark retrieved from Finch to see if there is indeed any useful materials in it. In Bonnie's ambush, she is able to convince Gracie to return home with her. Gracie's sense of comfort at home is short lived. Alison and Donnie's new illicit drug business hits a potential snag when Donnie believes he is being followed by who he thinks is the police. His tail does eventually reveal himself, he who surprises Alison. Cosima follows two research leads, the most immediate being Duncan's book, the notes which she and Scott try to decipher. But she also ... Written by Huggo

Mark has captured Sarah and taken her to the Castor compound, where she is housed in a cell adjacent to Helena's. However, it's not quite the reunion that Sarah was hoping in that Helena will not forgive Sarah for turning her in, she unaware that it was actually Mrs. S who made the arrangement. Although Helena will not open up, Sarah knows that Helena knows the detailed workings of the compound and thus probably knows a way out. Beyond Helena, Sarah has to decide who she can trust, the list of people who includes Paul. Meanwhile, Cosima goes on her date with Shay, the two who met on an Internet dating site. There seems to be a connection between the two. Cosima, however, is unaware that there are more people on their date than meets the eye. And now that she has miscarried, Gracie has been shunned by her mother and excommunicated. Because of Sarah, Gracie turns to Art for help, he in turn who believes that Mrs. S and Felix are better equipped to look after her. Felix in particular is ... Written by Huggo

Sarah is all alone at the Castor compound now that Helena has managed to escape, although Rudy is tasked with locating her, she who they believe cannot get far being in the middle of the desert. Sarah is also not feeling well, knowing that Coady and her team have done something to her. Sarah no longer trusts Paul, but behind the scenes he is trying to discover exactly what secret work Coady seems to be working on. Mrs. S and Felix are at different stages of worry about missing Sarah's whereabouts. Felix goes to someone who he believes can help, he doing whatever he needs to get the information about Sarah's whereabouts. Delphine returns on news that Sarah is missing, her return which does have an effect on Cosima's burgeoning relationship with Shay. Delphine, Cosima and Scott try to discover what is affecting Gracie. And Alison and Donnie are basking in the success of their new drug business, which Donnie may take a bit too far. Along with Jason who probably knows more about the ... Written by Huggo

Sarah and Helena have managed to escape from the Castor compound, and arranging with Mrs. S are awaiting Benjamin's arrival in the Mexican desert to retrieve them. However, they are surprised to see that their retriever is Mrs. S herself. This meeting allows for a showdown between Helena and Mrs. S, the former who wants to kill the latter for selling her out. With Cosima's new relationship with Shay being strong, Cosima is having problems dealing with Delphine, whether it be on a professional or personal level. Cosima feels like betraying a request by Delphine without telling her. On the drug dealing front, Alison and Donnie are having problems with Alison's mother, Connie, in the agreement to buy her store, which they need as a money laundering front. While Donnie and Jason meet with their supplier, Pouchy, for the first time together, Alison attends an all candidates meeting at the school. All of Alison's problems come to a head at the same time in a potentially very public setting.... Written by Huggo

The clone club have made the decision that Helena and Gracie should now be the responsibility of the Hendrixes, which does not sit well with Donnie. Both Alison and Donnie believe they have to address the issue of Jason, and his romantic interest in Alison, although they take different approaches in dealing with the situation. Cosima continues to have problems in what seems like her love/hate relationship with Delphine, who she no longer trusts. Cosima and Sarah have not divulged to Delphine that Scott has been talking to Rachel about deciphering Duncan's code in the book. Rachel wants to make a deal with Sarah, which involves her, Felix and another sister who Sarah wants to remain outside the fold of knowledge about the clones, while various sides have differing opinions about what to do with and about Rachel. Castor may play a factor in the equation about Duncan's code, which may also affect Denise's well being. Written by Huggo

Based on what Rachel had deciphered of Duncan's code, Sarah, Felix and Mrs. S believe the answer to finding the Castor original is in London, where they head to Mrs. S' old stomping grounds prior to Sarah and Felix entering her life. Help from Mrs. S' old network of friends doesn't turn out quite the way they expect, which leads to diverging opinions on what to do next. Cosima now believes what Delphine had intimated, that Shay is a mole for Castor. Cosima and Delphine individually have to decide what to do based on that belief. Donnie's physical altercation with Jason jeopardizes the business partnership between Jason and the Hendrixes, with the resulting actions profoundly affecting Helena. Helena proves to be much more resourceful in resolving the matter to her satisfaction than Donnie imagines. Written by Huggo

With Art's help, Sarah, Mrs. S and Felix are able to hide the Castor and Leda original, Mrs. S' own mother Kendall Malone, although she is somewhat of a hostile participant in the matter. Mrs. S is blunt that she has no hesitation in killing her mother if Castor even gets close to finding out their hideout, both Castor and Topside who they know will soon find out where they are hiding. Coady's approach in finding the Castor original is to go after the one sister who is out in the open, namely Alison who, along with Donnie, is in the midst of the school trustee election. As Helena can't be included in the public aspects of election day, Donnie has what he believes is the ultimate gift for Helena to keep her preoccupied. With Topside, Delphine believes she has a deal that will satisfy Ferdinand and Topside's needs in the Leda project. With all these pieces, Rachel becomes an increasingly important player. And Shay may not be able to forgive Cosima for what Delphine did, both ... Written by Huggo