Season 4

Complete listed story — includes the ending

1. Echoes

This episode's plot summary may be too long or excessively detailed. Please help improve it by removing unnecessary details and making it more concise. ( September 2020 ) ( Learn how and when to remove this message ) Clarke confides in Bellamy about A.L.I.E.'s warning of the nuclear power plants melting down and the human race surviving only six more months. In the aftermath of the battle, it turns out that the people Lexa killed to protect Clarke in the City of Light are actually dead, leading the people of Polis to declare both Wanheda and Skaikru their enemies; Echo leads the Ice Nation warriors against Skaikru and begins to take the city by force. To stop her, Clarke and Abby manage to save King Roan from his bullet wound. When Roan awakens, Echo attempts to convince him to kill Clarke, but Clarke gives Roan the Flame; he declares himself ruler of the thirteen clans until the Flame chooses another commander, and he announces their peace with Skaikru. Murphy and Emori run away from everyone to be together; Clarke, Bellamy and Jaha leave Polis and return to Arkadia to decide their next move in their fight against the radiation that's coming. Elsewhere at Arkadia, Raven attempts to determine exactly what kind of damage the radiation will deliver while Jasper's suicide attempt is unknowingly interrupted by Monty. Using Arkadia's sensors and historical records, Raven determines that A.L.I.E. was telling the truth as radiation levels are already beginning to rise and the power plants were only designed to last for one hundred years without maintenance. At the same time, in Egypt, a radioactive pyroclastic wave kills two people, an effect of the approaching apocalypse.

2. Heavy Lies the Crown

This episode's plot summary may be too long or excessively detailed. Please help improve it by removing unnecessary details and making it more concise. ( September 2020 ) ( Learn how and when to remove this message ) Ilian, a grounder who was under A.L.I.E.'s influence, kills his family to convince his mother to take the chip but the AI is destroyed before he can be forced to kill himself too. Soon after when his mother dies, she tells him to avenge her. In Polis, Kane and Abby sleep together, while Ambassador Raphael, together with Ilian, plans to challenge Roan. Roan prepares for battle despite being too weak from his injury. Kane and Octavia attempt to deter Raphael, but he refuses. Octavia later assassinates him, making it seem as if Raphael died of natural causes. At Arkadia, Raven, Clarke, Bellamy, Monty, Harper, Bryan, and Miller devise a plan to restore Alpha Station to survive the radiation and acquire a hydro-generator for water from Farm Station which is in the Ice Nation. Grounders meet them there and eventually agree to give them the generator. However, they find many of their own as slaves and vote amongst them to use the generator to make an explosion to free them. The leader of the grounders, Tybe, is the man who murdered Monty's father. Monty then frees the slaves who then beat Tybe to death. Everyone returns to Arkadia but with no way of supplying water for everyone. Clarke tells the people of the radiation crisis and they all agree to work together.

3. The Four Horsemen

Jaha leads Clarke and Bellamy on a search for a bunker built by the Second Dawn doomsday cult that could be used to survive the coming death wave; however, they discover that the bunker wasn't shielded properly and everyone inside had died. A group of grounders, including Nyko and Luna, arrive at Arkadia with signs of acute radiation syndrome (ARS) from eating contaminated fish. Abby wants to use their radiation medicine, but Raven, who is now in charge of rationing, stops her. Murphy steals it and gives it to Abby anyway. The new Flamekeeper, Gaia, steals the Flame from King Roan, but before Octavia kills her Indra stops her, stating that she is her estranged daughter. Using a decoy, Octavia tells Roan the Flame was destroyed. At the same time, Ilian leads grounders in destroying all of the technology in Polis. Arkadia can only house 100 people for the next 5 years to ride out the radiation. Clarke writes a list and includes Bellamy as number 99, and he writes her name for the 100th spot. Luna is the only person who does not die from the ARS, which makes Abby realize that Luna's body is rejecting the radiation because of her Nightblood, offering a possible solution for everyone.

4. A Lie Guarded

In Polis, Kane and Bellamy are sentenced to die when Roan ends the alliance with both Skaikru and Trikru. Abby, Raven, Murphy and Luna return to A.L.I.E.'s island to discover how they can use Luna's Nightblood to save the human race from the radiation. Drones fire on them, resulting in Nyko's death and driving Luna to her breaking point. Echo hunts down Octavia and after a sword fight, Octavia is stabbed and falls off a cliff, but survives. Also, Monty and Jasper discover and expose Clarke's list of 100 names forcing Jaha to resolve the conflict.

5. The Tinder Box

Raven and Abby discover that because they were released from A.L.I.E.'s control via EMP instead of when Clarke pulled the kill switch, that they have leftover knowledge from the AI in their brains. They learn that Becca was making Nightblood on the Ark and after they find a rocket, they prepare to go back to the Ark to make Nightblood for the survival of the human race. Ilian brings Octavia to Arkadia to sneak his way in. Octavia warns them of Roan's planned takeover of the ship and Clarke goes to negotiate with him. They eventually agree to share Arkadia 50–50 until Ilian blows up the ship and they all watch their last chance of survival burn to the ground.

6. We Will Rise

Clarke, Bellamy, and Roan go on a road trip to deliver ten barrels of hydrazine fuel to Raven for her trip to space to make Nightblood. The residents of Arkadia band against Ilian and want to execute him for destroying the ship but Kane tries to resolve the conflict peacefully. However, Octavia holds a gun to Ilian's head but is stopped at the last minute by Kane who points out that Lincoln had been murdered in a similar fashion; she has an emotional breakdown and leaves. Also, Clarke lets her lover, Niylah, stay at Arkadia for the time being. During the drive, a Trikru attack on Clarke, Bellamy, and Roan results in one of the hydrazine barrels being pierced by an arrow and emptied. Later as Raven hears the news, she suffers a seizure.

7. Gimme Shelter

The black rain begins to fall, and as the Sky People shelter in the remains of Arkadia, Bellamy tries to rescue a father and son trapped outside, but is unable to reach them. Octavia and Ilian take refuge in a cave, but when he tries to get her to open up about Lincoln, she tries to go into the black rain and kill herself, but he stops her. They have sex, and she decides to go with him back to his family's abandoned farm. At the underground lab on Becca's island, Abby tells Clarke about her new plan to implant Luna's bone marrow into a test subject to see if it can create immunity, but to test this they would need to use a huge dose of radiation on the subject, which could kill them. When a grounder thief breaks into Becca's mansion and is captured, Emori identifies him as her nemesis Baylis. She intends to kill him, but Clarke decides to use him as the test subject. Emori later admits to Murphy that the thief is not Baylis, and that she lied to save herself from being sacrificed.

8. God Complex

After the first test kills the thief, Emori's lie is discovered and she is taken prisoner, with the intention of using her as the next subject. Murphy also has to be tied up when he tries to stop them, and Luna is knocked out by Roan when she tries to leave. Clarke changes her mind and injects herself with Luna's bone marrow, becoming a Nightblood, but before she can subject herself to the radiation, Abby destroys the machine, with her hallucinations having convinced her that Clarke would die. In Arkadia, Jaha overhears Niylah use a phrase associated with the cult who built the shelter, and believes that the shelter he found was a decoy. Suspecting Gaia may have information that could lead to the real shelter, he, Kane and Monty go to Polis, where the Tree People are fighting the Ice Nation for control. Gaia helps them deduce that the shelter is beneath Polis, and they find it using a talisman found at the decoy shelter.

9. DNR

Clarke struggles to keep the peace in Polis after word of Jaha's discovery of the shelter spreads, which makes other clans, including Roan's and Indra's, want a part of the shelter for their own people. To secure the peace, Clarke agrees to become the new Commander, but the revelation of where her Nightblood comes from causes Roan to decide to hold a final conclave instead to determine which clan will control the bunker. At Arkadia, Jasper and Bellamy get into an argument when Jasper and other like-minded youth of the original 100 want to stay behind to celebrate the end of the world, while Bellamy wants to lead the remainder of Arkadia's 400-plus population to the shelter before the death wave arrives in less than six days and wipes out all life. Raven decides to stay behind at the lab as she is haunted by Becca's hallucination urging her to continue the space rocket repairs as Murphy and Emori decide to head out to the shelter. Elsewhere, Octavia struggles to adjust to living at Ilian's farm until a brutal and lethal encounter with three hostile grounders make her realize that she cannot run away from her past.

10. Die All, Die Merrily

The clans hold a fight to the death at Polis to determine which clan will receive the shelter. Octavia, Roan, and Ilian represent their respective clans. Luna also fights, but explains she will not let anyone into the shelter if she wins. During the fight, Echo is discovered to be cheating without Roan's knowledge and is subsequently banished by Roan as punishment. Octavia decides to ally with Ilian, but he is killed with an arrow to his neck by Echo. Later, only three warriors are left; Octavia teams up with Roan to take on Luna, but a storm of black rain arrives which puts both of them at a disadvantage against Luna, who is a Nightblood. Although Luna kills Roan, Octavia eventually defeats Luna and becomes the winning champion. She decides to share the shelter equally with the clans, allowing 100 survivors from each clan. It is then discovered that members of Skaikru settled in the bunker during the battle and sealed the door.

11. The Other Side

With little sense of the situation outside of the bunker, Clarke and Jaha refuse to open the door and risk the future of humanity. Abby helps Bellamy unlock the door and Clarke is unable to use force to stop him from opening it. Echo is stopped from exposing Skaikru's treachery when Octavia threatens to reveal her cheating and banishment. Octavia bans Echo from the bunker. By Octavia's decision, Clarke is left with 12 hours to banish over 300 of her people to the surface, possibly leaving too few skilled workers to maintain the bunker. At Arkadia, Monty tries to save the others to no avail. The partygoers commit mass suicide using a fatal overdose of the hallucinogenic Jobi Nuts previously encountered by the 100 shortly after their landing on Earth, Jasper dying in a devastated Monty's arms. However, Harper decides that she loves Monty enough to live. At the same time, a rapidly-deteriorating Raven is convinced to undergo a suicidal spacewalk by her hallucination of Becca before a hallucination of Sinclair appears to give her new hope. With Sinclair's help, Raven purges A.L.I.E.'s residual code from her brain by temporarily killing herself, "rebooting" her brain and curing her condition.

12. The Chosen

Jaha and Kane disagree over how to handle their grim reality when they must choose only 100 out of their 400 people to shelter at the Second Dawn bunker to make room for the rest of the 1,200 grounders, who want to place their own survivors there as well. It all leads to holding a lottery which threatens to tear the fragile plans apart. Abby asks Kane to let her give up her place to make space for others. Eventually, the two men gas their people and use Clarke's list to decide who will stay. Clarke leads Bellamy, Murphy, and Emori to save Raven, who still is at the lab with Murphy and Emori planning to shelter in the lighthouse bunker Murphy was trapped in. A group of grounders attacks them, but Echo saves them; Clarke gives Emori her suit after Emori's is damaged, but Clarke suffers from the radiation, suggesting that her Nightblood failed. With no time to return to Polis, Monty and Harper are called to transport the group to the lab where they come up with a plan to go to the remnants of the Ark in space to survive instead.

13. Praimfaya

As the death wave hits Polis and the Second Dawn bunker, 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. Monty is incapacitated after going out with Murphy to obtain an oxygen generator for installation in the Ark from the lighthouse bunker. With only 25 minutes before the death wave hits, Clarke uses a satellite tower to power up the Ark remotely, but complications force her to miss the rocket launch. Clarke ultimately succeeds and runs back 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. The death wave destroys the Earth, scorching most of the planet bare. Six years and seven days later, Clarke is revealed to have survived the death wave due to her Nightblood along with a young Nightblood girl, Madi. While Clarke tries to make contact with the Ark, a spacecraft lands on Earth in the only fertile valley left. The sign on the side of the ship identifies it as a prison transport, alarming Clarke.