The episode begins in Polis with a shot of Octavia in a room by herself. Bellamy walks in to speak with her. He tells her that she doesn't need to fight, but she's willing to accept death. She then stops Bellamy from saying anything else and walks out.
Octavia walks out into a courtyard after Gaia summons her. It's official that Octavia will fight for Skaikru. Gaia then summons Ilian since he will be fighting for his clan as well. Octavia asks him if he's trying to prove anything, but Ilian responds to her by saying that he's there for his clan and not her. After Gaia explains the rules of the conclave and what will happen at its' conclusion, Luna suddenly forces her way through the crowd, naming herself as the last of her clan. Gaia derides her as the coward who ran from her own conclave, but Luna declares flatly that she won't be running from this one. She then accepts her sigil as the warrior of her clan. However, since she's the last of her clan, Gaia questions who is she fighting for. Luna declares that she's fighting for death, to the shock of everyone present; if she wins, she will allow no one to enter the bunker, resulting in the extinction of the human race.
Back inside a battle prep room in Polis, we see Indra approach Octavia. She begins to pep talk Octavia and says that it's okay to be afraid. Indra then pulls out her own sword and offers it to Octavia as a gift. Octavia wants to know why she's doing that since it may mean the end of her people. However, Indra assures Octavia that she is one of her people. She concludes her pep talk by telling Octavia that she's in control of who she really fights for. They embrace.
Moments later in a courtyard, Clarke is speaking with Bellamy and Kane. Clarke expresses concern about Luna's entry since she's a specialist at this sort of combat. Jaha then expresses concern about what may happen even if Octavia wins the Final Conclave. Kane assures Jaha that they will have Octavia ready. Jaha suggests they get the bunker ready anyway, implying that Skaikru should be focused on their survival and that the grounders will not honor Skaikru's position in the bunker if Octavia somehow wins. Kane disagrees, saying if they try to cheat they will lose the bunker for certain; the conclave is sacred, and the Grounders will honor that. "Like it or not, we're all Grounders now." he remarks.
Clarke approaches Roan and tells him that they can't let Luna win. She asks if he can beat her and Echo chimes in by saying, "Of course he can." Roan then tells Clarke that he's done with alliances. He also tells her to get off of the battlefield before she dishonors her people once again. Roan does believe he will win, but claims that if he is destined to die on the battlfield, he doesn't care who enters the bunker. Clarke shoots back that that is the difference between him and her; he is fighting for 'honor' while she is fighting for the surival of the human race, even if that doesn't include her people. As Clarke leaves, Echo gives her a peculiar look and then walks off.
Back inside the battle prep room, Kane approaches Octavia with tips for what to do against each warrior. Bellamy then approaches her with a strategy to try and lay low, which she is already good at from her years in hiding on the Ark. This will allow the strongest fighters to take each other out. She then realizes that it's true that she doesn't have to kill every warrior; she only needs to kill the last one.
War drums sound and the various warriors go to their starting points in the maze of Polis, each marked by the battle flag of their clan. As they walk, Fio, the Trikru champion, compliments Octavia's skill, remarking that it is a pity he will have to kill her. Seconds later, we hear battle horns playing, signaling the beginning of the conclave. Several warriors let out primal screams and run into battle.
At first, we see Roan in a battle with a large man wielding a giant hammer. Octavia is running around trying to observe the action without being seen. However, Fio spots her her and gives chase. Octavia knocks down various pieces of debris to slow him down as she runs, finally ducking behind a piece of metal sheeting near Roan's battle; Fio unknowingly climbs right over her, then stops to observe Roan. Moments later, we see Roan cut down the large man and kill him with his own hammer. Fio then attacks Roan with a pair of long knives. However, Roan gains the upper hand quickly, stabbing him with his sword. He then picks up the token of the fallen warrior and yells, "Trikru has fallen!" Gaia sees this and immediately becomes sad. She announces the death of the two soldiers and then runs over to Indra to hug her. It appears that Trikru's place inside the Second Dawn Bunker is no longer an option.
Octavia enters the armory; as she warms her hands on a brazier, Luna enters and approaches her. Octavia says that Lincoln would be ashamed of Luna, but Luna claims Lincoln was a fool for believing that all of humanity could act as one people; she points out that, at the end of the world, humanity chooses to fight to the death instead of working together. Octavia reminds Luna that she used to believe people were worth saving, but Luna says she was wrong. The cruelty she suffered at Skaikru's hands in the name of survival made her conclud, that humanity is inherently cruel, violent and selfish. Octavia claimed Lincoln wasn't, and that she loved him for his faith in humanity, but Luna claims that, by choosing to fight in the conclave for a specific group, Octavia is disrespecting that same faith and proving she is no different from the worst of humanity.
Luna mockingly repeats Octavia's words back at her, "Lincoln would be ashamed of you", and attacks. It is immediately clear that Luna is the better fighter; she forces Octavia back and lands several blows, finally knocking her down. Before she can make a killing blow, Octavia throws a fistfull of grit and sand into her eyes. As Luna clears her vision, Octavia slashes a rope holding a set of metal pipes that drops on Luna, knocking her down. As Octavia flees, Luna wipes Nightblood from her forehead and screams that she can't hide forever.
A few seconds later, we see Octavia run into a room to tend to a wound. Ilian then breaks inside of the room and tells her that he's not there to kill her. He says that she's not his enemy. However, she claims that she will kill him the next time that she sees him. It's clear that tension is at an all-time high during this conclave to end all conclaves.
Back at the tower in Polis, we see Bellamy checking out the action. He notices that one of the fighters dies from an arrow from a masked figure. Noticing that Echo has disappeared, he realizes that she is cheating and he goes to do something about it. Kane tries to stop him, saying if he's seen on the battlefield Octavia will be executed and Skaikru loses the bunker, but Bellamy insists that Ice Nation has two fighters in the conclave. It's not fair and he intends to stop it. However, Kane tells him to wait until it's dark so no one catches him.
Back on the battlefield, Octavia has several fighters approach her. However, Ilian jumps into the fray and helps her defeat them. Octavia tells him to stay away, but Ilian refuses to listen. Suddenly, an arrow pierces Ilian through his neck — one fired by Echo. Octavia drags him away from the line of fire and mercifully ends his life. It appears that Ilian's fight is finally over.
Once it becomes nightfall, we see Bellamy sneaking around Polis while trying to find Echo. He then gets a good view of her and proceeds to get closer. However, he notices one of the conclave fighters coming around a corner and hides. Moments later, he watches Luna kill the warrior in less than five seconds. As Luna leaves, Octavia is seen following her discreetly; Echo sees her and aims an arrow at her, but Bellamy's appearance startles her and causes her to misfire. Bellamy knocks her down, rips off her mask and begins choking her as Octavia runs up the stairs to investigate the commotion. Roan suddenly appears and kicks Bellamy off of Echo, saying he heard both of them on the street. Bellamy says he was trying to stop Echo and Roan demands that she explain herself as Octavia watches them, unseen. Echo says that she's doing what's best for their people, but Roan refuses to taint his honor for the sake of victory, as his mother would have done. He angrily banishes her from the Ice Nation, ordering her to leave the battlefield without being seen or she will doom Azgheda anyway. Turning to Bellamy, he warns him he could have Octavia executed now by simply calling for a scout, "but what fun would that be?" He allows Bellamy to leave without anyone seeing him. As he goes, Bellamy warns Roan not to underestimate his sister.
Seconds later, we see Gaia announce that only four warriors remain within the conclave. Kane then approaches Indra and apologizes about Trikru. She then comments about how Octavia is doing well and Kane thanks her for that.
Roan is attacked by Octavia, but dodges her attack. As they circle each other, he accuses her of betrayal, but she points out that, due to her prior loyalty to Indra, he didn't leave her much of a choice. Acknowledging her point, Roan sheathes his sword and offers a temporary truce; one of them needs to win to ensure humanity survives, but he doesn't believe either of them can defeat Luna one-on-one. Octavia asks what happens once Luna is dead, to which Roan smiles grimly and replies "May the best warrior win."; until then, they are one clan. After a moment, Octavia grips his arm and nods. As Bellamy sneaks off the battlefiend, he is chloroformed and dragged away by a masked figure.
Roan and Octavia hear the sounds of battle and circle towards it from two directions. Roan arrives just in time to see Luna throw her pike and impale her opponent through the back; when he approaches, she simply picks up her opponent's twin swords. He takes the token from the body and taunts Luna to take it from him as Octavia approaches her from the side. Roan and Octavia attack together, but Luna's skill enables her to fight them simultaneously; she inflicts minor wounds on both of them. Roan finally manages to knock her down with a punch while she is driving Octavia back, but as he raises his sword for the kill, a clap of thunder sounds. Black rain starts to fall; Octavia runs for cover as it burns her skin, yelling at Roan to do the same.
Luna, immune to the irradiated rain due to her Nightblood, gets up and attacks the disoriented Roan, slashing him across the stomach. Disarming him, she declares that his fight is over. Roan makes a last desperate attack, pinning Luna's arms and forcing her own sword against her throat, but before he can kill her, Luna headbutts him, twists free and slashes him again. Dropping her sword, she grabs Roan by the hair and shoves him headfirst into a nearby fountain, drowning him as Octavia watches in shock. She flees as Luna takes the tokens from Roan's neck and pursues her, mockingly declaring that "the King is dead."
Luna stalks Octavia into an abandoned building, entering a room with various hiding places; she kicks open a door, peering under various shelves and tables until she spots a thin trail of blood leading to a wardrobe. She admits that at one time, what Octavia said about her was true; that if you showed people an alternative to the endless killing, the darkness in them would fade, just as hers did when she stopped blaming herself for killing her brother. However, Luna admits that, on the day of her conclave, in the moment when she knew only one of them could survive, she still wanted it to be her; what scared her into leaving the conclave wasn't grief, but horror that her own dark survival urges were no different from anyone elses'; that darkness can surface again in anyone, no matter how deeply they bury it. As she finishes speaking, Luna stops in front of the wardrobe and stabs it twice, declaring that she is the darkness, and this is the end. She then throws the doors open, but the wardrobe is empty. Octavia suddenly stabs her through the stomach from behind. As Luna dies, Octavia tells her that she was wrong: there are people worth saving, just not her.
Closing Luna's eyes, Octavia tells her her fight is over and takes the rest of the tokens; she is the champion of the conclave. Gaia announces her as the winner and that the Second Dawn Bunker belongs to Skaikru. However, Octavia says that she's not only fighting for Skaikru, but for everyone. As a result, she announces that everyone will share the Second Dawn Bunker together. This leads to everyone chanting the word "Together!" However, Octavia is wondering where her brother is since Bellamy isn't around for her victory speech.
Moments later, we see Bellamy wake up inside of the bunker. It then becomes clear that Jaha and Clarke are responsible for his abduction. Along with the abduction, they end up locking the entrance to the bunker. This leads Indra to saying, "Skaikru has betrayed us all" as the episode concludes.