- Writers: John Fawcett, Graeme Manson, Alex Levine, Kim Coghill, Andrew De Angelis, Jeff Detsky, Adam Higgs, Bob Mackowycz Jr., Elize Morgan, Peter Rowley, Rebecca Sernasie
- Stars: Ari Millen , Dylan Bruce , Evelyne Brochu , Jordan Gavaris , Josh Vokey , Kevin Hanchard , Kristian Bruun , Maria Doyle Kennedy , Skyler Wexler , Tatiana Maslany
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 believes the Castor clones may also ultimately provide some useful biological information. Felix wants to help Cosima forget about Delphine by being her online dating wingman. And Helena tries to fool her captors, in the process find out more about where she is being held.