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 Ring. 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. Now safely aboard the Ark Bellamy and Raven vow to survive in order to honor Clarke's memory. 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 Eligius Mining Corporation.
Tropes in this episode:
- Body Horror:
- In order to get the oxygen device out of the Lighthouse Monty is forced to take off his bulky gloves in order to reach the circulatory in the back. It leaves his hands with horrific radiation burns that cause him to collapse from the pain.
- Getting caught with the full blast of Praimfaya causes Clarke's whole body to be covered in radiation burns and she collapses after throwing up blood. Thankfully the nightblood in her system seems to have worked and by the Time Skip she's back to normal.
- Book Ends:
- The series began with Clarke as a prisoner being transported to the ground by her people in order to determine if it was survivable 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.
- Broken Faceplate: While Clarke is running back to the bunker after activating the satellite she ends up tripping and smashing a hole in her radiation suits protective faceplate just to make the situation more dire.
- 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 culture's equivalent of seppuku since she believes that there 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.
- "Eureka!" Moment: While Raven is having a Heroic BSoD moment when the rockets communication network won't work and laments that she might know what to do if she still had A.L.I.E.'s code in her head Bellamy tells her that they don't need A.L.I.E. on the Ark just her. This makes Raven realize that they can use the same method A.L.I.E. used to transmit herself onto the Ark in order to activate the Ring's power on the ground.
- 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 Ark 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.
- No One Gets Left Behind: While he is forced to abandon Monty at first when he collapses, once Murphy gets the oxygen device to Raven, he and Bellamy are quick to go back and rescue him before the death wave hits.
- Outrun the Fireball: Once Clarke is stuck on the ground she makes a mad dash to the bunker while the death wave is right on her tail. She ends up reaching the bunker just as the wave of fire and death is about to reach her. She doesn't completely miss it and suffers from some series radiation burns but thanks to her nightblood she is able to survive the process.
- Race Against the Clock: After Polis is hit by the death wave Raven calculates that the group has ninety minutes to get the oxygen generator from the Lighthouse, perform a preflight check that usually would take six hours, reconfigure a cockpit meant for two to hold eight people, and load the cargo hold with enough food so that the group doesn't starve before the algae farm is up and running. And predictably things end up going wrong while the group are doing this which makes the job even harder.
- Time Skip: After the Praimfaya wave hits the earth and Bellamy's group successfully reaches The Ark the story cuts ahead to six years and seven days later as Clarke, along with a Nightblood 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.
