Octavia and Bellamy say their goodbyes over radio but are cut off. Before they are, Bellamy reassures Octavia of her leadership capabilities. Indra also encourages her. O puts on the symbol of the commander and gives a speech of hope to everyone in the bunker as the death wave hits above them. Clarke isn't able to say goodbye to her mother before they're cut off and Bellamy comforts her. Clarke makes Bellamy promise to use his brain when leading if she dies like in her mother's vision.
Meanwhile, on Becca's island, the group scrambles to prepare for launch, condensing an hours-long process into just 90 minutes. Raven sends Monty and Murphy to retrieve the device needed for oxygen aboard the Ark, while the others remain behind to prepare the ship. Monty and Murphy run into an issue when Monty needs to take his gloves off in order to remove the machinery, severely injuring his hands with the radiation. Monty passes out and Murphy is forced to leave him behind, carrying back the machine to the lab.
In the lab, Raven runs diagnostic tests and realizes that comms are down -- there is no way to communicate with the Ark, meaning they can't get the power back up and open the hangar door to get inside. Raven is despondent, thinking all hope is lost. Bellamy gives her a pep talk and Raven realizes that ALIE was able to connect with the Ark before. She determines that they can use a nearby satellite tower to connect with the Ark and open the hangar door. She, Clarke, and Bellamy head off to do that while Emori, Echo, and Harper remain behind to work on equipping the rocket to hold 8 people.
Murphy runs up with machinery and finds Raven, Clarke, and Bellamy as Clarke and Bellamy are preparing to make the run to the satellite to connect with and power up the Ark. He tells them about Monty, and he and Bellamy run back to retrieve him. Clarke goes to the satellite by herself, with Raven explaining that she doesn't have a lot of time to get it running and get back to the lab in time for launch.
Murphy and Bellamy find Monty and get him back to the lab, where Raven and the other women are making final preparations. They realize Clarke is not back yet but they are running out of time before the death wave hits.
When Clarke gets to the satellite, she finds that it needs to be manually overridden -- meaning she needs to climb to the very top of the tower. She realizes this means she will not make it to the rocket in time and accepts her fate in order to save her friends. After some issues getting the satellite to connect and to turn, she gets it to work in the nick of time, as her friends (who successfully launched into space) are running out of oxygen in their tanks. She gets down from the tower and runs back to the lab, collapsing with severe radiation burns (just like Abby's vision) and apparently dead.
In space, Raven spacewalks to open the hangar door once Clarke powers up the Ark. The group, who are all rapidly running out of oxygen, scramble to set up the oxygenator before passing out. They all pass out but Bellamy managed to put in the oxygenator correctly and they all come to once air starts circulating. Raven and Bellamy mourn Clarke's apparent death but agree to work together to survive so she won't have died in vain.
Six years and seven days pass...
On Earth, Clarke is alive, her nightblood having effectively protected her from dying from radiation poisoning. She radios Bellamy every day, attempting to make contact, but has never been able to. She wonders why they have not come back down to earth yet, noting that it is now safe for them to do so. She hasn't been able to get in contact with the people in the bunker either or to get them out because of all the rubble. Clarke sees a spaceship coming down, excitedly thinking it is her friends. She goes to wake up Maddie, her young Nightblood protege and companion.
They quickly realize it's not the ship they were expecting to see and is instead a prisoner ship. Clarke prepares for the worst, sending Maddie for the guns in case they need to fight the strangers.