Three months after the conflict with Mount Weather Kane learns that a bounty has been put on Clarke's head, threatening to end the fragile truce between the Sky People and the Grounder tribes. Elsewhere Clarke makes her way on her own, and Murphy emerges from a bunker to find Jaha transformed.
Kane's recon group crosses paths with some familiar faces while searching for Clarke, who has been captured by a member of the dangerous Ice Nation. Murphy and his friend Emori reconsider their part in Jaha's plan, while Abby takes a patient into Mount Weather to try and save his life.
Clarke is confronted by Lexa's past betrayal when the Grounders ask the Sky People to join their coalition. Bellamy learns that the Ice Nation has sent an assassin to the summit between clan leaders, and at Mount Weather Raven leads a team to try and unlock the missile defense system.
In the wake of a devastating attack Queen Nia of the Ice Nation calls for a vote of no confidence in Lexa, prompting a fight to the death between Lexa and Roan. Marcus and Abby come into conflict with Pike over Arkadia's ongoing alliance with the Grounders.
Pike leads a massacre of a Grounder encampment that threatens to destroy the fragile peace, and Clarke infiltrates Arkadia to try and make things right. Meanwhile Jaha arrives in the settlement with a spiritual message, and Murphy and Emori make trouble on the road.
The arrival of a prisoner forces Clarke to make a difficult choice about her enemy's fate, while Octavia does recon for Kane to learn Chancellor Pike's long-term plans for Arkadia and the Grounders living nearby. Jaha and Alie give Raven an important task.
Lexa attempts to maintain a tenuous peace among the twelve clans, ordering a blockade to contain Arkadia's forces -- while Titus has plans of his own for a captive Murphy. Ninety-seven years in the past, a research scientist goes to great lengths to save her technology.
Having been surrounded by a Grounder blockade Arkadia hangs on the brink of civil war, as Kane rallies his people to undermine Pike's hold. Raven recruits Jasper to help her break into the Chancellor's office, only to discover that her alliance with Alie has come with a price.
Clarke and Murphy find themselves in the middle of a bloody struggle for power as the Grounders select a new leader. After Pike orders the execution of Kane and the other insurgents, Bellamy goes to Octavia with an offer to help rescue them.
As Raven fights to be free of Alie's control, Jaha shows the A.I. a new way to sway the people of Arkadia. Monty must flee the city, while elsewhere Ontari makes use of Murphy's counsel as she struggles to gain control of the alliance in the absence of the Fire.
While Clarke, Jasper, and the others try to free Raven from Alie's control, the A.I. forces her to turn the tables on her captors. Monty is forced to make a difficult choice, and Clarke realizes just what it is that she has in her possession.
Clarke and her friends return to Arkadia and find the city abandoned, and are soon attacked by a mysterious, masked foe. Murphy is reunited with Emori inside Polis, and Jaha makes an unexpected power play.
After Pike is handed over to the Grounders Kane discovers that Jana and Alie have taken over, and is tortured when he refuses to take the Key. Clarke, Bellamy, Octavia, and Jasper follow Lincoln's directions to try and find Luna, and Murphy remembers Pike's harsh survival training on board the Ark.
Bellamy, Clarke, and Octavia try to convince Luna to join their cause, only to see her come under direct attack from the enemy. Elsewhere Murphy, Pike, and Indra escape confinement and try to disrupt Alie's power source, and Raven makes a discovery in Alie's code.
Clarke enlists the help of King Roan of the Ice Nation in an attempt to infiltrate Alie's stronghold, only to fall into the enemy's trap. Elsewhere, Raven works to rebuild her backdoor into Alie's program while under threat from a mole.
With no options left Clarke takes drastic actions to try and retrieve the code to Alie's kill switch, while her friends work to secure the tower from the onslaught of Alie's forces.
