At Polis, Clarke sketches Lexa while Lexa is napping. Lexa jolts awake from a nightmare -- the Commanders before her speak to her in her sleep and she saw their deaths. She interprets it as a warning against her ceasefire, which they would see as a betrayal of their legacy. Clarke and Lexa are interrupted by Titus and several man bringing in a box, from Roan, which is meant as a demonstration of Azgeda's loyalty. Inside the box is Carl Emerson, the last remaining Mountain Man. He lunges at Clarke and attacks her before being pulled off and imprisoned by Lexa's men.

Octavia spies on Hannah and more of Pike's people as they collect soil and water samples near the river on Pike's orders. She radios back to Kane to let him know. They wonder what Pike is up to. They spot a Grounder child and attempt to kill him, to prevent him from telling his people that he saw them. Octavia saves the child and reports back to Kane.

Abby tests Raven and sees that her pain is gone. Raven tells Abby that Jaha gave her the key to the City of Light, not drugs. Abby is suspicious. Abby reluctantly clears Raven for work now that her pain is gone, with the caveat that she'll rescind it if anything abnormal comes through in Raven's bloodwork.

Kane and Miller go to break into the Chancellor's office. Kane distracts Pike and Bellamy by talking about Jaha's chips while Miller plants a bug in the office so that they can listen in on Pike's meetings. 

Abby and Jasper watch as Jaha hands out more of the chips. Jasper notes that his followers seem happy and Abby notices that Jaha's number is growing. She advises Jasper to hold off on joining them until she figures out what the chips are exactly.

Kane and Octavia listen in as Pike meets with Monroe, Bellamy, Monty, Hannah and his other followers to discuss the plans for "expansion and salvation." Monty questions wiping out the Grounder village at Sector 4 in order to make way for their farmland. Hannah explains that the soil near the river is perfect for farming soybeans and corn. Monty and Bellamy voice concerns and are against wiping out the Grounder village. Pike explains that it must be done or the Sky People will starve to death within a year. Bellamy concurs that they will do what needs to be done. Octavia is horrified and rushes off to warn the Grounder villagers.

Lexa meets with Clarke to discuss Carl Emerson's fate. Titus is for killing him for his part in the deaths at Mount Weather. Clarke agrees, to Lexa's surprise. Lexa points out Clarke's hypocrisy, in opting for vengeance only when the crime was against her own Sky People. Clarke claims that killing Emerson will end a war, whereas retaliating against Pike will start one. Lexa gives Clarke until the night to decide whether Emerson will be banished or killed by a thousand cuts at Clarke's hand.

Miller brings Octavia a horse. Octavia prepares to leave to warn the Grounder village to stop the attack. Miller questions whether her warning will work. Octavia reminds him that if Lexa finds out Pike slaughtered another village of Grounders, she will not hold back on declaring war. Miller agrees and Octavia goes off to stop the attack.

Jaha and ALIE recruit a happy Raven to find a dormant or unfinished AI program (the second generation of her code) that was on the Ark, that ALIE has been searching for for a long time. Raven agrees to get ALIE access to the mainframe and leaves. ALIE wonders why Jaha has not told Raven about ALIE's true nature and Jaha points out that they lost Murphy when Murphy knew what she was. He mentions that they cannot expect success in asking Raven to find an upgrade for a computer program that ended the world.

Kane tries to talk sense into Hannah and Bellamy, who are loading up weaponry for the attack on the Grounder village in Sector 4. Miller hugs his boyfriend goodbye as Bryan heads off to join the attack.

Octavia goes to the village and warns the assembled villagers to leave or else Skaikru will kill all of them. She is attacked by the villagers who identify her as Skaikru and don't believe her. The stop the attack on her after the boy she saved earlier steps forward on her behalf. 

Abby and Jackson discuss the unlikelihood of Raven's pain disappearing with Jackson. Jackson confirms that there is nothing unusual about Raven's tests. Abby asks Jackson to leave when Kane arrives. Kane voices his guilt over having allowed Pike to be elected and sending kids out to fight his battles. Kane tells Abby that Bellamy is the key in Clarke's absence. Abby kisses Kane to comfort him.

Semet, one of the Grounders, agrees to take Octavia's advice, since they are no match for Sky People guns. Octavia notices the Grounders setting a trap. Semet tells Octavia that she does not know them and knocks her out.

Raven gets ALIE into the system so she can search for the AI. Before ALIE enters, she explains to Raven that the second AI would have been in space because ALIE's creator wanted a more secure work environment (because of ALIE). Jasper joins Raven. He confesses that he stole Finn's ashes and spread them near the dropship. He is surprised when Raven is not angry and asks her what she is on. Raven encourages him to join Jaha.

Clarke meets with Emerson. Emerson rails at her for having slaughtered so many at Mount Weather, including his two children. Clarke tells him that President Wallace gave her no choice. He tells her that he wants revenge, not mercy; he wants Clarke to suffer. Clarke leaves.

Clarke finds Titus waiting for her back in her room. He asks her to help him convince Lexa to retaliate against Skaikru, believing that the Grounders will not accept her decision against retaliation. He tells Clarke that he fears it will get Lexa killed. Clarke turns him down, saying she cannot help him in a way that will lead to the death of her people.

Jasper meets with Jaha. Jaha encourages Jasper to take the chip, telling him that it will work to remove his emotional pain. Abby interrupts, stopping Jasper right before he ingests it. She asks him to explain what exactly the chip is. With ALIE's go ahead, he does so. Abby asks to test the chip for side effects, asking if Jaha would have given it to Wells without testing it first. ALIE reminds Jaha of who Wells is. When Jaha doesn't recognize Wells' name at first, Abby is alarmed. She sends Jasper away and tells Jaha she is shutting down his operation until she tests the chip. She takes the chip and leaves. Jaha tells ALIE that they cannot allow Abby to stop them. Jackson appears and is able to see ALIE -- he tells them that he will keep an eye on Abby.

Octavia comes to and realizes that the Grounders set a trap for the Sky People with poison smoke. She gets a safe distance away and shouts to warn the approaching Sky People of the trap. Most of the Sky People manage to get away but Monroe succumbs to the poison and dies. The group is distraught and Hannah tells Bellamy that his sister did this and that there are traitors in the camp passing her inside information. Octavia is knocked down and captured by Semet and his people.

Lexa gathers her people to witness as Clarke enacts the death by a thousand cuts upon Emerson. At the last moment, Clarke decides against Emerson's death, announcing that Emerson's death may bring her peace, but it's a peace she doesn't deserve. Titus reacts, trying to command Lexa to kill Emerson anyway. Lexa shuts Titus down and gives a speech to the assembled Grounders that mercy is a new way to a long-lasting peace and a better future.

Pike and Bellamy discuss Monroe's death and Octavia's involvement. Pike mentions that the poison gas also poisoned the soil. Bellamy is sure that they both already know who is the traitor at Arkadia -- Kane. Pike asks Bellamy to get proof. Bellamy agrees.

Titus tortures a bound Murphy. Murphy insists that he does not have any more information on Clarke. Titus asks him for information on the ALIE chip instead. 

ALIE and Raven report that they could not find Becca's AI. ALIE is confused because she was sure that Becca was on the Ark but the AI is not on any of the 12 stations' systems. Jaha explains the story of the 13th station that was blasted out of the sky by the 12 others, inspiring Unity Day, when the 12 stations came together. The 13th station was known as Polaris.

In the background, we see a piece of what is clearly the remnant of a space station, with remnants of the word Polaris written on it. Polis is Polaris.