Praimfaya has officially begun. The death wave hits Polis and the Second Dawn bunker, while Clarke, Bellamy, Raven, Murphy, Emori, Monty, Harper and Echo gather at the lab to ready the rocket to travel to the remains of the Ark, the Riing. Monty is injured after going out with Murphy to obtain an oxygen generator for the Ring, as the originals were removed when the Ark crashed. During modifications to the rocket, the communication system shorts out, meaning the Ring cannot be radioed to turn on. With only 90 minutes before the death wave hits, Clarke decides to stay behind to climb to the top of an antenna tower to realign the dish in order to send the command manually prior to launch. Clarke, however, is unable to make it to the rocket prior to launch, and is trapped on the ground. The rocket's launch is successful, and Raven spacewalks to the Ark to dock the rocket pod. After programming power for the Ark, Clarke runs to the lab with the death wave right behind her, but upon arriving, she is revealed to have been affected by the radiation. On the Ark, the group almost runs out of air before the oxygen generator is installed. Six years and seven days later, Clarke is revealed to have survived the death wave along with a young Nightblood girl, in apparently the only still living forest on Earth. While Clarke tries to make contact with the Ark, a spacecraft lands on Earth, labelled as belonging to the Elgius Mining Corporation.
Tropes in this episode:
- Book-Ends: The series began with Clarke being transported to the ground by her people in order to determine if it was liveable and running afoul of the Grounders already living there. This season ends with a new transport carrying prisoners arriving on the ground and this time Clarke herself is the Grounder.
- Season 1 ended with Clarke closing the dropship door on Bellamy and Finn, believing they were dead. Season 4 ended with Bellamy closing the rocket door on Clarke, believing her to be dead.
- Critical Annoyance: Oxygen level critical...oxygen level critical...repeats for several minutes as the rocket group works to get the ring up and running.
- Driven to Suicide: Echo almost commits her cultures equivalent of seppuku since she believes that their is nowhere else left for her. Bellamy is able to snap her out of it and point out that they need her strength to survive the next five years.
- Friendship Moment: After a confrontation that the two have earlier in the episode Monty hugs Murphy once he finds out that the latter went back with help and rescued him after securing the Oxygenation device. Monty even comments that he doesn't hate Murphy anymore.
- Heroic Sacrifice: Clarke ends up stuck on the ground desperately trying to get a satellite in alignment in order to activate the power on The Arc so that her group can survive. Ultimately she can't return to the shuttle in time before take off. Although miraculously she survives.
- The Heart: Clarke explicitly calls Bellamy the heart in their partnership, with her being the head. When she believes she's going to die, she tells him that he needs to be both.
- Time Skip: After the Praimfaya wave hits the earth and Bellamy's group successfully reaches The Arc the story cuts ahead to six years and seven days later as Clarke, along with a Night Blood child named Madi, are seemingly the only survivors on earth as neither the bunker nor Bellamy's group have made it back to the ground. And then suddenly an entirely new squad of people arrive from the sky.
- Visual Pun: Bellamy and Raven share Jaha's Baton (a drink) on the Ring. They are assuming leadership from the presumed-deceased Clarke while literally passing the Baton between them.
- You Are in Command Now: Octavia fully becomes the leader of Wonkru even signified by Indra giving her Lexa's old Heda ornament.
- Raven and Bellamy are in charge on the Ring.