Felix and Sarah try to hide Seth's body, but Art shows up at the apartment and catches them in the middle of clean up.

Cosima theorizes that the Castor clones have a genetic design flaw similar to the Leda clones that's neurological. They plan to do an autopsy to examine his brain for further proof.

Art tells Sarah he has a lead on the Prolethean Castor clone, Mark. 

Mark and Gracie enjoy their honeymoon on the run, until Mark admits that he was sent to spy on her father and recover stolen scientific information. 

Back in the city, Art and Sarah track down the Prolethean midwife and pump her for information about Mark and Helena. She tells them that both Helena and Gracie are pregnant, and Art gets a lead on the car Mark and Gracie escaped in. 

Gracie volunteers to recover the stolen documents from Finch, her father's accomplice. 

At the Castor base, Paul and Dr. Coady discuss the glitch in the clones. Coady asks Paul to buy them time with the mysterious 'Director' so that she can cure the glitch.

Cosima and Scott perform an autopsy on Seth in Felix's bathroom. 

Inside the Dyad Institute, Rachel recovers from her injuries and tries to recover her full range of speech. She learns that Delphine faked her death. 

The midwife tells Gracie's mother where Mark might have taken her, tipping off the Proletheans to their whereabouts. 

Art confesses that he was in love with Beth, and those feelings are why he's so invested in helping Sarah and her sisters.

Sarah find Gracie alone, and she reveals that Mark is a clone. Meanwhile, Mark tortures Finch for information about the original clone samples that Henrick stole. 

Cosima figures out that the Castor clones original DNA is too similar to the Leda original DNA, meaning that both sets of clones are brother and sister. Sarah finds Mark at the farm and tries to reason with him, but Bonnie shows up and kills him.