Jaha, Murphy, Craig, and Richards are rowing across a sea in search of the City of Light. Craig stops rowing in frustration that they're not even sure where they're going. Richards suddenly spots land in the distance and they cheer. Their boat is suddenly knocked by something beneath the water, tossing Richards into the water. As Murphy tries to help him, a creature grabs Richards and drags him underneath the water, injuring Murphy in the process. Craig starts to freak out as Jaha yells at him to row. Murphy tells Jaha he can row just as Jaha tosses Craig into the water to the sea creature and the sea creature swallows him whole. Jaha tells Murphy he did it because Murphy can row.
Down in the mines underneath Mount Weather, Octavia is waiting by herself for Bellamy to open the intake door. An alarm sounds and a body is dropped down a chute into a mining cart. Octavia sees Fox, dead from bone marrow drilling. Clarke comes running up, telling Octavia that Lexa and the Grounder army has left. Octavia and Clarke then get in a fight because Clarke is desperate to get into Mount Weather and will bring unwanted attention on them. Suddenly, the door opens and Bellamy appears with Monty, Jasper, and Maya and everybody hugs. Clarke asks Bellamy if he has a plan and he tells her no, but they can speak to Dante Wallace. Maya's oxygen tank beeps, warning her she is running low on oxygen. They split up with Bellamy, Clarke, and Monty going after Dante and Octavia going with Jasper and Maya to get her to Level 5 before she runs out of oxygen.
Back at a Grounder camp, Indra approaches the tree Lincoln is tied to. Lincoln asks how she can do this and Indra tells him that she swore loyalty to the Commander. She places a knife beside him, telling him Octavia has already made her choice and now he has to choose whether to stay here or march on to Mount Weather, but if he does he will be breaking the Grounder alliance with the Mountain Men. Lincoln takes the knife and heads toward Mount Weather and Octavia.
In Mount Weather, the residents have gathered on Level 5. Cage Wallace is told he is needed in the dorm where all of the Sky People are tied up as they extract bone marrow from a Delinquent. Emerson tells Cage that they suffered losses and he is the only one left who has received the bone marrow treatment. Emerson then reveals the four additional Sky People they captured outside the Mountain: Monroe, Sgt. Miller, Abby, and Marcus Kane. The Delinquent on the table dies and they pick Raven to be used next. They strap Raven to the gurney and Raven bites the face of one of the doctors. The guards use a shock baton on her and they get her tied down and begin drilling.
In Dante's room in Mount Weather Quarantine, Clarke, Bellamy, and Monty come to him for help. Dante tells them that there is no one in the Command Center watching because everyone is trapped on Level 5. Clarke explains how they did everything they could to keep the Mountain Men safe and he needs to help them. Dante refuses to help but they take him with them anyway to the Command Center.
Jaha and Murphy have finally reached the shore. Jaha offers Murphy help and Murphy tells him he doesn't want anything from him because of what Jaha did to Craig. Murphy tells him he's a survivor and is done following Jaha. A drone appears and Murphy tells Jaha to go chase the drone. Jaha promises to come back for Murphy before taking off after the drone.
Monty breaks them into the Command Center as Dante tells Clarke that he's not with his people because it's his responsibility to "bear it so they don't have to." Bellamy realizes that it was Dante who set up the alliance with Lexa.
Jasper, Maya, and Octavia arrive on Level 5 just as Maya's oxygen runs out. Jasper tells them he needs to kill Cage in order for Maya to be able to survive.
In the Command Center, Bellamy sees Raven strapped to the table in the dorm room while Clarke spots Emerson in the Mess Hall. She calls him over the radio and tells him to give the radio to Cage. Clarke tells Cage she has his father and tells him she'll kill Dante if he doesn't let her people go. Dante tells Cage to "stay the course" and Clarke raises up her gun and aims it at Dante. Cage tells his dad he'll take care of their people and Clarke shoots Dante dead. Clarke then tells Cage she will not stop until her people are free and will irradiate Level 5 if he doesn't let them go. Cage orders Emerson to go to the Command Center and kill them. Bellamy asks Monty to deactivate Emerson's key card as they watch Cage head toward the dorm. Clarke tells Monty to get it set up so they can irradiate Level 5 if they have to. In the dorm, Cage orders Raven to be removed from the table and has Abby put on instead. Kane tells them no one has to die because the Sky People can donate it. Cage tells him that it will never happen and they can't all survive as they begin drilling into Abby. Bellamy warns Clarke there is no going back if they do this.
Maya returns with Lee to where Jasper and Octavia are waiting. Octavia gives Jasper a knife and explains to him how to cut Cage's throat. Jasper and Maya kiss goodbye and Jasper tells her he loves her. He then leaves with Lee to go after Cage.
Murphy awakens the next morning to see a lighthouse. He walks up to it and uncovers a solar panel causing music starts playing within the lighthouse and Murphy goes to investigate, finding his way inside what appears to be a fully stocked bunker. He helps himself to some MREs and liquor, enjoying his "promised land."
Octavia and Maya sit and wait for the all clear. They are soon interrupted by a kissing couple who run away and alert the Mount Weather guards. Octavia chases after them and takes out two Mount Weather guards with her sword and newly learned grounder moves. Bellamy sees their predicament just as Emerson arrives outside the Command Center. At the same time, Lee is walking Jasper into the dorm while Octavia and Maya are soon chased into the Mess Hall and are quickly surrounded by Mount Weather guards. Monty finishes the settings to irradiate Level 5 as Emerson gets ready to blow the door to the Command Center. Jasper is walking over to kill Cage while Abby is unconscious on the table. Bellamy watches as Octavia and Maya are caught in the Mess Hall. Clarke reaches for the lever and Bellamy places his hand on top of hers, saying, "together," before they pull the lever.
The Mount Weather residents begin to succumb to the radiation. Emerson realizes what they have done and takes off running. Octavia sits with Maya until Jasper runs over. Maya tells Jasper, "none of us is innocent." Octavia runs into the dorm and begins freeing the Sky People as Kane runs over to Abby to help her.
Clarke, Bellamy, and Monty walk through the Mess Hall and all of the deceased residents of Mount Weather. Jasper is cradling a dead Maya and asks them what they did. He asks Monty how he could have let this happen. Clarke is reunited with her mother in the dorm and tells her she tried to be the good guy. Abby tells her that "maybe there are no good guys." Sgt. Miller is reunited with his son as Octavia asks where Cage went.
Cage is traveling through the woods when Lincoln finds him. Cage tries to control him with his tone generator and brings out a dose of the Reaper drug but Lincoln fights through the high frequency and slices Cage's hand off. Lincoln overcomes his addiction to the red drug and injects it into Cage instead, killing him.
The next day, the Sky People return to Camp Jaha. Marcus and Abby enter first with Abby on a stretcher while Kane holds her hand. The Millers enter next, followed by Octavia and Lincoln, holding hands. Harper is next, followed by Monroe and Jasper. Raven and Wick enter, with Raven stopping Jasper and returning his goggles. Bellamy watches at the gate as Monty gives Clarke a hug before entering Camp Jaha. Clarke tells Bellamy to have a drink for her and Bellamy realizes she's leaving. He tells her, "if you need forgiveness, I'll give you that. You're forgiven." She tells him, "I bear it so they don't have to," before hugging him and kissing him on the cheek in goodbye, telling him, "may we meet again." As Bellamy turns back to Camp Jaha, he replies, "may we meet again."
At the lighthouse, Murphy has found a TV and pushes play. A home movie shot on 5/10/2052 in the same bunker appears onscreen. Murphy watches as the man explains how he lost control and how "she" got the launch codes. He apologizes before shooting himself dead.
Meanwhile, Jaha has chased the drone to a hilltop mansion where hundreds of other drones float above it. He enters the mansion and encounters A.L.I.E., an artificial intelligence, who tells him that she has been waiting for him since she received his "gift." She takes him to another room and tells him they have work to do as she reveals the nuclear warhead Jaha came down to earth in.