The episode unfolds with a radio conversation between Bellamy and Octavia. Bellamy assures Octavia they will meet again. Octavia says that she'll be waiting, under the floor, and Bellamy responds that she's not that little girl anymore. Octavia then admits that she doesn't know if she's ready for everything. She feels that she's not a leader, but Bellamy tells her that she gives people hope when there is none. They joke for a little bit, then she says that she loves him. Suddenly, their radio communication cuts off before Bellamy could say he loves her back. A devastated Bellamy then says "May we meet again."
Clarke walks in after Bellamy and Octavia's conversation, to which Bellamy tells her that the radio is dead, therefore, she won't be able to say goodbye to her mother. Clarke becomes emotional as she hugs Bellamy and cries on his shoulder. Bellamy comforts her for a while before they are interrupted as Murphy calls them.
Back at the Second Dawn Bunker, Indra enters Octavia's quarters. She encourages Octavia and says that she needs to lead. Octavia says that she's not a commander. However, Indra says that the time of commanders and the flame has passed — It is Octavia's time now and offers to help. Indra then opens her hand and shows Octavia the same forehead emblem that Lexa wore. This officially marks Octavia as their leader.
Octavia stands before everyone, the emblem on her forehead, as she addresses everyone inside the Second Dawn Bunker. She informs the people of the arrival of Praimfaya. She ends the speech with the words, "from the ashes we will rise".
Back at Becca's lab, Bellamy, Clarke, Raven, Monty, Harper, Murphy, Emori, and Echo watch the radiation destroy Polis through their last drone feed. Raven then begins calculations in her head and realizes that she'll need to manually dock the ship in the hangar bay. She also tells everyone that they need to be off the ground at least 20 minutes before the death wave hits. Though the situation seems grim, Bellamy offers some optimism. Moments later, Raven Presses a button and a timer is set for 90 minutes - the time left until the death wave reaches them.
Murphy and Monty discuss Jasper's death as they search for the oxygenator. Murphy makes a snide remark about Jasper taking a coward's way out and an enraged Monty grabs him. Murphy tells him to be careful about ripping his suit. Then Monty tells Murphy the only thing he cares about is surviving. However, their quarreling comes to an end when they find a large panel at Becca's bunker with the scrubber. In order for them to get it out in one piece, Monty decides to take off his gloves to dislodge it. The moment his hands are exposed to radiation, his hands quickly start to burn as he screams in agony.
Meanwhile, at Becca's lab, Clarke discusses their food rations for their space plan with Echo. A few minutes later, Clarke and Bellamy have a conversation. Clarke tells Bellamy about her concerns regarding her mother's visions. Bellamy's doesn't believe the visions will come true and tries to reassure Clarke, but Clarke begs him to listen. She tells Bellamy that regardless of the stupid things that he's done, it's admirable that it was always to protect Octavia. Clarke says that he'll need to use his brain more than his heart in order to survive the next five years on the Ark. Bellamy then tells Clarke that what he has her for. From a distance, the rocket is damaged, as Raven yells. Alarmed, Bellamy and Clarke run towards the rocket, as smoke comes out of an area in the spaceship. Raven says there's not enough time and she's pushing too hard. She then commands the computer to assess the damage. They are informed that the communication system is down. Bellamy asks Raven to talk to them and she says that they're not going anywhere. She then tells the spaceship to abort the mission.
Moments later, Bellamy asks her to explain and she says that there's not enough power. Clarke then asks her to think because they've seen Raven solve harder things. Raven then breaks down and says that she's not smart enough by herself. Bellamy then tries to console her and say that she can do it. Raven then remembers A.L.I.E.'s ability to transmit herself to the Ark. She then tells everyone to get back in the cockpit and asks the computer to resume the launch sequence.
Meanwhile, Monty and Murphy are carrying the oxygenator. Monty's hands are badly burnt by the radiation and Murphy helps him get his gloves on. They start to carry the machine and Murphy tries to distract him from the pain by asking him about Harper. Suddenly, Monty passes out and Murphy says that he's sorry. He then proceeds to drag the oxygenator back to Becca's lab by himself leaving Monty behind.
Outside Becca's lab, Raven instructs Bellamy and Clarke while pointing toward a tower. She gives a circuit to Clarke and gives instructions on how to transmit the signal to turn the power on in the Ark. Murphy appears with the oxygenator, struggling to carry it, as a concerned Bellamy approaches him. Bellamy is forced to go and get an unconscious Monty, leaving Clarke to plug in the circuit board herself. Raven then hands a bag to Clarke and says that she has 10 minutes to get from the tower to the lab once she completes her mission. Inside Becca's lab, Raven searches for Echo. Echo hides in a corner as she puts white paint on her face.
Back outside, Monty wakes up and realizes that there are only 14 minutes left to return to the lab. Murphy and Bellamy then arrive to save him. Murphy tells him that he got the oxygenator over to the lab. This leads to Monty embracing Murphy, telling him that he may not hate him anymore.
The action switches back to Clarke as she sees the tower and runs towards it. She opens the bag and takes the circuit board. Clarke sees the sensor that she needs to connect it to and hooks up everything. However, she's unable to get it working from the ground. She attempts to radio Raven but communications are down. Clarke then finds manual instructions and says, "My fight is over" as she begins to climb the tower towards the satellite.
Back at Becca's lab, Bellamy and Murphy are carrying Monty in. Harper hugs him and Bellamy wants to know where Clarke is. He also wants to know where Echo is. Just as he asks for Echo, she cuts her hand and put her bloody hand-print on her stomach. She then attempts to stab herself in the stomach. However, Bellamy runs in and stops her. He tells her that she's strong and needs to go with them to the Ark. Raven comes in tells them that there are two minutes until launch. Raven hands her a suit and tells her to put it on. When Bellamy asks about Clarke, Raven says they'll wait as long as they can.
Back at the satellite tower, Clarke nearly falls off the tower as she ascends it. She looks at the radiation wave rapidly approaching on the horizon. It's imperative that she hurry and find a way to transmit the power signal.
The action switches back to Raven telling Bellamy that it's now or never to launch. Bellamy reluctantly walks into the cockpit. Emori asks that they give Clarke another minute. However, they all decide that Clarke would want them to leave. They initiate countdown and they take off without Clarke. Clarke then watches as the rocket takes off and continues to climb the tower.
We see everyone bracing to release the ship from the rocket thrusters and the computer confirms that the separation is complete. Raven says that everyone should be getting a view of the Ring soon. However, when they see it, they realize that the power isn't on. Bellamy asks if Raven's ready for her space walk and she proceeds to do it. She needs to make sure that she's in a position to get the Ark's door open once Clarke gets the power on.
Back at the satellite tower, Clarke gets to the control panel at the top. Unfortunately, she gets the same result as she did on the ground. The computer recommends a manual override and the situation is getting extremely desperate for Clarke.
In space, Raven floats over to a door and sees that her oxygen is down to 18 percent. She attaches a power conduit to the door and awaits Clarke to get the power on. At this moment, we see Clarke physically attempting to get the satellite dish to turn to get it back online. She eventually succeeds and then the control panel says that it's searching for a signal. Suddenly, it shuts off as Praimfaya is virtually breathing down Clarke's neck. She proceeds to descend the tower and begins running for the lab. However, she falls and cracks her helmet. She gets inside Becca's lab and takes off her helmet, but her face is burned from the radiation. This scene ends with her falling and passing out.
Then, Murphy, Emori, Harper, Monty, Raven, Bellamy, and Echo get onto the Ark, but Raven is low on oxygen. Murphy and Emori decide to share theirs along with everyone else. Meanwhile, Monty instructs Bellamy to connect the oxygen scrubber to the conduits on the Ark. Suddenly, Monty passes out, then so do Emori and Murphy. Bellamy hits a switch and everyone passes out. A second later, the oxygen vents turn on and everyone begins to revive.
Bellamy looks down at a destructing Earth which resembles a fireball more than an inhabitable planet. Raven walks up behind him and says that Clarke saved them again. Bellamy says that he won't let her die in vain and Raven agrees. They continue watching in silence.
6 Years and 7 days later
Clarke indeed did survive Praimfaya. There she sits ontop of the rover, breathing in the fresh air as it rains. She gets off the rover as she walks toward the cliff, sitting on a broken tree bark. She gatheres the radio and satellite dish as she sits down, as she looks across the land. She radio calls Bellamy and says that despite not knowing if he's alive, radioing him keeps her sane. Clarke then continues by saying that it's been safe to come down for a year. She says that the Second Dawn bunker has gone silent as well. She has tried reaching the bunker several times, but there's also too much rubble to really know if anyone is alive.
Clarke continues to leave her message until she notices a pod coming down from the sky. She believes it's her friends and excitement fills her eyes. Clarke runs over to the rover and tells a Nightblood child named Madi to wake up. Madi questions Clarke about the ship. She wonders why Clarke told her that the ship would be small when it's clearly large. Clarke then tells her to run inside and grab her sniper rifle. As the ship gets closer, Clarke points the rifle towards the ship and looks through the scope. She sees the label marked on the ship that reads "Eligius Corporation" and "Gagarin Prisoner Transport". Madi starts waving her arms frantically in the air, so as to alert the people on the ship that they are there. Alarmed about the labels she saw on the ship, Clarke tells Madi to go and retrive the guns — all of them.
Clarke Griffin: Please, Bellamy, I need you to hear this. We've been through a lot together, you and I. I didn't like you at first. That's no secret. But even then, every stupid thing you did, was to protect your sister. She didn't always see that, but I did.
Clarke Griffin: You've got such a big heart, Bellamy. People follow you. You inspire them because of this. (points to his heart) But the only way to make sure we survive, is if you use this too. (points to his head)
Bellamy Blake: I've got you for that.
Bellamy Blake: We die. I left her behind, and we all die anyways.
Raven Reyes: She saved us again. Think we can do this without her?
Bellamy Blake: If we don't, she died in vain, and I'm not going to let that happen.
Lindsey Morgan stated in an interview that this episode was going to be stressful.
She said "It's quite a ride. It doesn't stop from beginning to the end… You're going to get really sweaty. It's a lot of stress."
Jason Rothenberg stated in an interview with TVLine, in the scene when Monty's hands get burned, Christopher Larkin who plays Monty actually lost his other glove, but Christopher kept going on with the scene. Same as Richard Harmon who plays Murphy, they continued filming until they found Christopher another glove for the scene.
Tasya Teles stated in an interview that the way Echo scrambled to Bellamy and ripped off his helmet to allow Bellamy to breathe, it wasn't in the script. Tasya and Bob Morley brought the idea to Dean White who directed the episode, Dean thought it was a great idea. 
According to the prop building crew, hazmat suits were the worst for the cast because the suits are uncomfortable and claustrophobic. The wearer can't see and can't talk.
Raven's space suit was very heavy for Lindsey to wear.