Cage and Dr. Tsing experiment on one of their own by sending Keenan out into the environment after a treatment from one of the 47. She seems to be doing well until she doesn't. In the rain, she begins to suffer radiation poisoning. Cage wants to let her back in, but Dr. Tsing insists they need to know how long Keenan can last outside. It's a sacrifice for the greater good of their community according to the doctor.
Dr. Tsing tells Cage the blood treatment is not enough to cure them permanently. In order to do that, she needs to take the bone marrow from the 47, which means the Mountain Men would live and the 47 would die. She wants Cage to convince his father.
Cage takes her father outside after a treatment to remind him of what they are missing in the hope that his father will approve the bone marrow plan. Dante refuses. He says that it would corrupt their legacy. Despite Dante's refusal, Dr. Tsing takes Harper and begins the new treatment.
While that was going on, Jasper, Monty and their crew break into Dante's office and find pictures of the Arkers. They know they are not alone. They also find a map of Mount Weather to use to find a way out.
At Camp Jaha, Jaha insists that everyone move out before the Grounders attack. Abby's not sure at first, but ends up agreeing with him after a public meeting. Clarke speaks out against the plan before going to the drop ship to help Lincoln. She's shocked to find out the Mountain Men not only worked with the Reapers, but actually created them.
She attempts to help Lincoln when he gets free from his restraints and attacks them. Octavia hits her love and knocks him unconscious. She leaves to get water and Nyko finds her. He's surprised to find out Lincoln's alive. He offers to help and starts to give LIncoln a medicine when Clarke realizes it's not to help but to kill Lincoln.
Finn shows up to tell them the plan is to leave before the Grounders attack. Nyko nearly strangles Finn to death and likely would have if Clarke didn't tase the Grounder. Lincoln stops breathing and Clarke performs CPR and saves him. Nyko is shocked that she was able to bring him back to life.
This gives Clarke the idea for peace between them and the Grounders. She goes to tell her mother her idea to offer to help the Grounders against the Mountain Men in exchange for a truce. Jaha remains committed to leaving even after Abby decides to go along with Clarke's plan. Jaha unsuccessfully tries to reclaim his position of Chancellor. Major Byrne supports Abby and puts Jaha in the stockades instead of Abby.
Clarke visits Lexa and makes her offer. They head to the drop ship to see Lincoln. When they get there, Abby hadn't been able to help Lincoln and he died. A battle almost breaks out in the drop ship. Abby uses the taser to jump start Lincoln's heart and he comes back to life. He recognizes Octavia. Lexa is impressed.
Clarke and Lexa agree to a truce with one condition. Lexa wants Finn. He must die to pay for the lives he took.