Lexa goes to see Clarke after respecting her wishes for a week to be left alone. Clarke is still angry with Lexa, and brings up her abandonment at Mount Weather. Lexa tells Clarke she will be returned to her people, but in exchange she wants Skaikru to become the 13th clan. Clarke refuses, noting that Lexa just wants her power because Clarke made Lexa look weak with her actions at Mount Weather. Lexa leaves.
Lexa meets with a member of the Ice Nation army, who refuses to bow before her. He asks Lexa why Wanheda is still alive, accusing her of weakness. She brings him to speak with her in private, saying she has a message for his queen. She kicks him off the tower at Polis, to his death, as a warning to anyone else questioning her orders.
Kane and Abby head into Polis to meet with Lexa. They argue about Abby's decision to moving people from Farm Station (an "exploratory group") into Mount Weather. Abby expresses doubt that the Grounders will allow them to leave with Clarke. Marcus promises they won't leave without Clarke.
Bellamy, Octavia, Raven, and Gina go to join Farm Station at Mount Weather. Bellamy expresses to Gina that he should be at the Summit to retrieve Clarke. Raven reminsisces with Gina about the time Raven "went rogue" on the Ark. When they arrive at Mount Weather, Pike greets them. Octavia is disgusted that they've moved in and she leaves. Sinclair finds Raven and demands that she get to work restoring power to the mountain.
Roan, also Lexa's prisoner, goes to talk to Clarke. He explains that Lexa also betrayed him and offers her help in getting revenge on Lexa. He has left a knife on her bed, for her to kill Lexa (since she can get much closer to Lexa than Roan can). He tells her that if she does so, she'll have a grateful ally in the Ice Queen.
Bellamy joins Octavia outside of Mount Weather. She tells him that moving into Mount Weather was a bad decision. Bellamy assures her that Lincoln and Nyko will make them see that inhabiting Mount Weather is not a bad thing. Octavia explains that once the situation is defused and Lincoln's kill order removed, they (she and Lincoln) will finally be able to leave Skaikru. She apologizes and explains to Bellamy that she doesn't fit in there. Bellamy accepts that.
They suddely see Echo, the Ice Nation grounder who was held in the cage next to Bellamy's at Mount Weather, being led by two Farm Station guards and rush towards her. Once released by the hesitant guards, she explains that the summit is a trap and she was trying to warn them. There is an assassin on his way and Bellamy's people will die.
Echo is brought into Mount Weather where Bellamy has her report what she discovered to Pike. Everyone in the Mountain is mobilized. Pike and Sinclair argue about using the missiles in the event of an attack. Raven explains that she can override the codes they are missing and get the missiles to launch. Gina asks Bellamy not to do anything stupidly heroic and kisses him goodbye.
The assassin prepares for the attack on the summit, cutting his hand.
Kane, Abby, and the others arrive at Polis. They look in awe at the central tower and observe the Grounders go about their lives in the central marketplace. A woman offers them food. Abby refuses but Kane takes it, communicating in the Grounder's language and offering her a patch from his jacket in exchange. Abby tries to give the Commander pin to Kane, realizing that he has a vision for peace. He refuses and they instead decide to hold an electron once they are back in Arkadia. Indra greets them and after Abby requests to see Clarke, she tells her that she'll see her soon.
Lexa helps train the young people in battle. She discusses the summit with her advisor. He cautions her that she appears weak because of Clarke and that Queen Nia of the Ice Nation is moving in on her. He tells her that the summit is a bad idea: her people will not accept Skaikru joining their coalition, and Skaikru intends to broker a treaty, not join the coalition. She refuses to let the threat of war dictate her actions. He advises her to kill Wanheda and take her power instead.
Gina, Sinclair, and Raven keep trying to crack the codes. Gina thinks that the president may have written it down somewhere, since the code was long, and goes to check.
Bellamy, Pike, Echo, and Octavia head to warn the others about the Summit attack. They find their own dead guards and Pike moves to blame Echo for her people having done that. Bellamy and Octavia get him to back off, noting that the attack is set to happen at sundown. The four go in through the tunnels so that they don't need to abandon their weapons per the entrance sign.
Clarke asks to see Lexa. Once Lexa arrives, Clarke moves to kill her with the knife. She hesitates and breaks down in tears, moving away from Lexa and dropping the knife. Lexa apologizes, having never intended to change Clarke into the person she is now. She tells Clarke that she is free to go and will be escorted to Abby. Clarke stops her, saying she has a better idea.
Clarke is brought to Kane and her mother. They embrace. Clarke reports back to Kane and Abby that Lexa has changed the terms of the summit: Skaikru needs to become the 13th clan. Abby claims that the Ice Nation moving on Lexa and killing her is not their concern. Kane disagrees, saying that if Lexa falls the coalition also falls. Abby reluctantly agrees and asks who stops the Ice Nation. Clarke says Wanheda will.
Clarke enters the summit dressed in full grounder gear as a woman sings the Grounder anthem. The assassin continues to anoint himself in blood. Clarke bows to Lexa, and all Skaikru and other clans' members present follow her lead. Per official decree, Kane is made to bear a brand identifying him as the leader of Skaikru. Bellamy, Pike, Octavia, and Echo enter Polis at the ground level and are ambushed. Bellamy kills the Grounder guards and Octavia chastises him for doing so. He looks at Pike and notes that he had to. The four climb up to the top of Polis to get to the summit.
As Lexa is explaining the plan for Skaikru to join the coalition, Pike, Bellamy, and Octavia burst in, claiming the summit is a trap set up by the Ice Nation. The assembled Grounders deny that there was any trap, noting that Skaikru, not Ice Nation, stormed Polis illegally bearing weapons. When asked where they got this information, the three notice that Echo is not there.
The assassin's alarm goes off and he marches into Mount Weather, not Polis, to begin the ambush.
Raven and Sinclair continue to attempt to crack the missile codes. Raven gives up despairingly. Sinclair insists that Raven doesn't give up. He asks her whether she talked to Abby about her leg surgery. He gives her a pep talk, insisting that she let Abby fix her leg. Raven worries that Abby can't. Sinclair encourages Raven to give Abby the chance.
Gina radios in, unable to find the code written down anywhere. Suddenly, the assassin attacks Gina, stabbing her repeatedly. Using codes written on his arm, he initiates a self destruct sequence. Gina collapses but is able to radio Sinclair and Raven telling them what happened and to find the assassin.
Sinclair chases after the assassin but the assassin gets the upper hand and nearly kills Sinclair. He is shot dead by Raven who tries to radio the codes to Gina, but Gina is dead. Raven tries to make it back to disarm the missiles, but is too late. Mount Weather explodes, killing everyone inside.
Raven radios over to Bellamy, tearfully explaining what happened. The Ice Nation delegate proclaims that Ice Nation did what Lexa was too weak to do. Lexa declares this an act of war and demands that the Ice Nation delegates, including Roan, be imprisoned. They are taken away. Abby and Kane prepare to return to Arkadia, in case that is the site of the next attack.
Lexa explains that one member of Skaikru must remain in Polis as a delegate. Clarke volunteers, to her mother's distress. Bellamy notes that Lexa betrayed them at Mount Weather and implores Clarke to come home to her people. Clarke apologizes and remains behind.
Clarke meets with Lexa, wondering how the assassin knew the Mount Weather missile codes. Lexa pledges fealty to Clarke, bowing to her, after Clarke warns Lexa to not betray her again.
Echo returns to Queen Nia and the Ice Nation and reports that she's got her war, thanks to the last living Mountain Man -- Carl Emerson, the Mount Weather guard. She also reports that the Ice Nation delegates, including Roan, are imprisoned. The Queen notes that they won't be for long.