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Clarke and her friends must risk everything to fight one last battle for survival, only to glimpse an even darker threat to the last living valley on Earth.

Octavia leads her people into war. While behind enemy lines, our heroes must overcome their differences to save Wonkru from extinction.

As Clarke races to save Abby, she learns more about the trials and tribulations Wonkru faced in the bunker, and the impossible decisions they were forced to make in the dark year.

Monty strives to show Wonkru an alternative to war, and to the valley itself. Meanwhile, Abby's health continues to deteriorate, along with McCreary's patience.

The growing fractures in Wonkru threaten to explode once and for all. Meanwhile, in Shadow Valley, Murphy starts a fire, unleashing catastrophic results.

Clarke's determination to protect Madi puts Bellamy in an impossible position.

Clarke and Bellamy make a startling discovery about Wonkru's battle plans as Echo risks her friendship with Raven to complete her mission.

Kane's attempt to prove himself useful tests Wonkru's allegiance to Octavia. Madi faces an unexpected threat inside Wonkru, forcing Clarke to make an unlikely ally.

Octavia leads her people towards Shallow Valley against the advice of Clarke and Bellamy. Meanwhile, Kane and Abby adjust to a new set of challenges.

Our heroes are forced to rely on the help of Shallow Valley's dangerous new inhabitants in order to save some of their own, with surprising results.

Bellamy leads the charge investigating a potential way home. Meanwhile, Clarke and Madi deal with the new, uncertain threat to their home.

Octavia is forced to take guidance from an unlikely ally when the future of the bunker and all those inside it is jeopardized.

Clarke struggles to survive on a desolate, scorched earth while her friends in space come across a long-awaited beacon of hope.