Helena takes shelter behind enemy lines, and Sarah and Art struggle to protect her and end the siege.
A flashback: Siobhan and a pregnant Sarah are sitting in their car, across the street from Planned Parenthood of Toronto. They are discussing abortion, and Siobhan is not sure that Sarah is ready to, or able to, properly raise a child.
Now: Sarah is helping Helena through the hallway of the Dyad basement, amidst the ringing of the alarm. They sneak by as Maddy Enger and another guard go towards the ringing alarmed door. Sarah and Helena get to a basement equipment room, and Helena can't go any further.
Maddy Enger gets to the door that Art had come in by and turns off the alarm. Art then comes up behind her and knocks her out. He hears from her radio the other guards calling for help, and takes the radio.
John Mathieson has reached Virginia Coady in Helena's birthing room, and helpers are giving her first aid. As Mathieson discusses the situation, he starts slurring his speech, and wavering, unsteady on his feet. One of the doctors goes to check him out, he may be having heart trouble. Coady orders everyone else to pack up to evacuate the building.
Helena is lying down in the basement equipment room, and she and Sarah agree they need some basic supplies if Helena is to give birth right there. Sarah goes to find supplies, leaving Helena armed with a screwdriver.
Sarah gets to a supply room and searches, when Coady and a guard enter; Sarah waits for them to leave, and Art shows up. Sarah sends Art to go help Helena.
Mathieson, still not doing well, orders the doctor to inject him with amphetamine, even though the doctor says it's not a good idea for someone in his condition.
Coady is searching the basement, and finds a door with blood drops in front of it; perhaps Helena went in there. She goes in, and finds Helena, having contractions. Coady goes to help her.
Mathieson is feeling better, and is ordering everyone to the roof for evacuation. Coady calls him to say she's found Helena, and he says he's on his way.
Art gets to the equipment room, and as he enters, Coady comes up behind him and gets his gun. She tells Art to assist Helena, she points him to instruments, but she's not getting close to Helena herself. At some point, when Art is between Helena and Coady, Helena allows Art to see the screwdriver she has.
Sarah gets to the original birthing room, and searches but finds nothing useful, it's all been collected for evacuation. Then Mathieson arrives there and starts to taunt Sarah as a useless clone.
Helena says she needs to push, and Art fakes: "there's bleeding, a lot of blood." This alarms Coady, who comes close to assess the situation, and when she's close enough, Art grabs the gun from her hand, and Helena stabs her through the throat and kills her.
Sarah and Mathieson struggle and fight, she shoots him, he weakens, then she kills him.
Sarah gets to the equipment room. (We see some flashback of Siobhan and Sarah at the abortion clinic, and Sarah declaring she will keep the baby.) Sarah and Art both assist Helena. (Now some flashbacks of Siobhan coaching Sarah as she gave birth to Kira.) The first twin is born, then the second, two fine-looking boys.
The scene then turns to Helena's apartment, the Hendrix's have had their garage remade into an independent apartment, kitchen and all, and Helena is there comforting the boys, each in his own crib. One is named Orange, and the other is Purple.
At Mrs. S's house, Sarah is studying for the high school equivalency test, as Cosima coaches her, and Kira comes in, needing her school lunch made. Kira goes off to school, just walking out the front door, no guards and no sign that anyone is worried about her.
At the Hendrix's, the back yard between the garage and the house is being set up for a big party, and Alison needs Donnie's help (there's a reference to his new job, regional manager for a concrete floor company). They wonder when Helena will give the boys real names.
At the lab, Cosima is collating lists of known clones, and Scott and Delphine are working on making more doses of the Leda cure, but they are worried that nobody knows how many Leda's there really are.
Sarah is poking around the house, boxing stuff, there are boxes all around, the house is for sale, Sarah is depressed about being in the house where her mother died. Felix comes to help, and Sarah's long-term plan is to just leave the house, and take Kira and go adventuring. Felix isn't sure that's what Kira wants.
Sarah gets to the high school equivalency test center, saying on the phone to Helena that she's on her way to the baby shower, first she needs to "finish" high school, then get a job. She looks at the testing center, then walks away.
The baby shower starts, all of the clones, families, and kids there, Helena unwrapping gifts, Scott flipping burgers. Many ask Sarah how the test went, and she just says "Fine". Some notice that Sarah still looks depressed and unsettled, selling the house is not a good sign, it's time to settle down, let the kids play together.
During this, Felix gets a call, and goes outside to a car, where Rachel is waiting. Felix assures her, her promises are kept, the family has the freedom they need, and the twins are fine. She knows she can't be accepted by the other clones, but wants to make a little bit of amends; she gives him a folder.
At night, with most of the families gone, Sarah, Cosima, Alison, and Helena sit in the back yard, drinking and/or smoking. Sarah admits she didn't go to the test, and feels she's a bad mother, lying to Kira, carrying around all the mistakes of her life. Alison pipes in with ways in which she has failed to be a proper mother, and Helena does likewise, and Cosima a little of the same. So they all share that they are scared with life, and mothering, and they all make mistakes.
Felix joins the sisters, and gives them the folder: it's a complete list of the 274 Leda clones, their locations, contact information, medical histories, all that they need to find and cure them. Helena shares the journal she had been writing, and starts to read it to them, she calls it Orphan Black. "I will start with the thread of my sestra, Sarah, who stepped off a train one day and met herself."
A few happy-ending scenes: Alison composing music, Donnie coming back from tennis; Delphine giving an innoculation to a Leda clone, Cosima making plans for them to find more in Brazil; Helena naming the boys Arthur and Donnie.
At Mrs. S's house, there are no boxes any more, but more of Felix's artwork around, and there is great bustle as the family gets ready to go out to a day at the lake, collecting swimming gear, fishing tackle, lunch. They all dash out the door to the car. The last one out is Sarah, who closes the door on the house. Her house.
- Tatiana Maslany as Sarah Manning/Cosima Niehaus/Alison Hendrix/Helena/Rachel Duncan/Camilla Torres
- Jordan Gavaris as Felix Dawkins
- Kevin Hanchard as Arthur Bell
- Kristian Bruun as Donnie Hendrix
- Josh Vokey as Scott Smith
- Maria Doyle Kennedy as Siobhan Sadler
- Skyler Wexler as Kira
- Stephen McHattie as P.T. Westmorland
- Kathryn Alexandre as Tatiana Maslany's Acting Double
- Kyra Harper as Dr. Virginia Coady
- Lauren Hammersley as Adele
- Elyse Levesque as Detective Enger
- Cynthia Galant as Charlotte
- Nicholas Rose as Colin
- Calwyn Shurgold as Hell Wizard
- Millie Davis as Gemma Hendrix
- Eileen Sword as Sister Irina
- Ted Dykstra as Doctor
- Ava Arrindell as Maya Bell
- Mike Shara as Dyad Guard #2
- Mark Sparks as Dyad Guard #3
- Bailey Corneal as Clone B
- Heidi Malley as Clone C
- John Nelles as Dialogue Coach
- The Hendrix garage is now renovated as a studio home for Helena and her sons.
- Art adopted Charlotte.
- Sarah and Kira live in S's house.
- Cosima and Delphine are traveling around the world to cure the LEDAs.
- Rachel is incognito, with her future uncertain.
- Coady and Westmoreland are dead.
- Felix is in a committed relationship with Colin.