Abby is determined to find a way to protect her people from a coming attack by the Grounders, even if it means heading into unknown territory and leaving some captives behind. A worried Bellamy convinces Clarke to go with him to the drop ship, where he and Octavia reveal a dangerous secret. Clarke comes up with a bold new plan to stop the Grounders' attack, leading Abby to a desperate decision. Meanwhile, at Mount Weather, Jasper and Monty begin to question the motives of their new friends, while Dr. Tsing conducts a deadly experiment to determine how to make use of the captives.

Clarke strikes a deal with Lexa and Indra. Abby and Kane begin to realize that decision making powers are out of their hands. A seething Raven is unable to control her emotions. A bold move threatens to destroy the newly formed alliance between the sky people and the Grounders, and a familiar face haunts Clarke. Meanwhile, back at Mount Weather, Monty comes up with a risky plan.