100 years in the future, when the Earth has been abandoned due to radioactivity, the last surviving humans live on an ark orbiting the planet — but the ark won't last forever. So the repressive regime picks 100 expendable juvenile delinquents to send down to Earth to see if the planet is still habitable.
Still reeling after receiving Monty’s message, a small group goes down to explore the mysterious new planet. Back on the Mothership, several members of Wonkru face the consequences of their decisions.
The team on the ground flights to survive the threat they face on the new planet. Meanwhile, Raven must join forces with an unlikely ally to save everyone on board the Mothership.
Clarke tries to win over the leaders of Sanctum in order to let her people stay. Meanwhile, Bellamy, Echo and Octavia discover a new threat while on a mission to retrieve the transport ship.
Clarke embraces the traditions of Sanctum and tries to make amends for her past actions.
Jordan investigates Sanctum. Meanwhile, Octavia and Diyoza discover the threats of the new planet firsthand. Lastly, Bellamy and Clarke butt heads.
Diyoza learns more about the mysterious Children of Gabriel while Abby continues searching for a way to save Kane.
Clarke’s past catches up to her.
Octavia and Diyoza make their way to the mysterious anomaly in search of the Old Man. Meanwhile, Murphy has an offer for Emori.
Bellamy must venture into enemy territory with an unlikely companion. Meanwhile, Octavia is forced to confront her past.
Russell seeks justice. Meanwhile, Gabriel must make a difficult choice. Lastly, the Blake siblings reunite.
Bellamy and Octavia must work together to save their friends. Echo is forced to face her past.
A special Naming Day changes everything in Sanctum. Gabriel comes face to face with an old friend.
Sanctum becomes a battleground between the devout and the non-believers. The mystery of the anomaly deepens.