The red sun derails Clarke's plans.

Clarke and her friends reckon with all that has happened only to find an unexpected threat looming.

Clarke and Octavia mount a desperate rescue mission as the Disciples close in on what they want.

Discovering that Jasper may still be alive, Clarke, Bellamy, Finn, Wells and Murphy head out to find him. On the Ark, Abby is determined to prove Earth is habitable, and enlists a mechanic to craft an escape pod.

97 years after a nuclear war, human kind is living in space. 100 juvenile delinquents are sent down to Earth to see if the planet is habitable.

After all the fighting and loss, Clarke and her friends have reached the final battle. But is humanity worthy of something greater?

Lexa tries to maintain peace and order within the clans, and Clarke uncovers a strange and game-changing truth. Meanwhile, a flashback takes us into the darker chapter of humanity’s past.

Kane is searching for a peaceful way to handle things but soon realizes he may be forced to resort to drastic measures. Meanwhile, Pike suspects that there may be a leak within the walls of Arkadia. Lastly, Raven has a plan and reaches out to Jasper for help.

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.

Clarke discovers a shocking truth, and Octavia is forced to make a decision that could have devastating consequences. Meanwhile, Kane and Abby share a moment.

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.

As a dangerous, acidic fog approaches, Clarke, Finn and Wells set out in search of a seaweed-like plant to make an antibiotic poultice for Jasper's wounds, while a vulnerable young girl follows when Bellamy takes a group out hunting for food.

A plan to contact the Ark is put in motion after Raven crash lands on Earth. Meanwhile, Abby exposes Kane's plan to reduce the population of the Ark.

Clarke and Finn are captured by Anya, who forces them to save the life of a victim of the explosion. Meanwhile, Raven deals with her split from Finn, and Kane fights to save the Ark and it's survivors.

Jaha employs a terrifying new method to convince Abby to join his cause, Kane is on a mission, and Bellamy is hit with a hard truth. Meanwhile, Monty finds himself in a precarious situation, and Jasper rushes to save one of his own.

Jaha returns to Polis, and Murphy has a surprise encounter. Meanwhile, Octavia uncovers a clue.

Clarke and her friends struggle with how to proceed after the fate of the world is revealed.

Bellamy, Clarke and Finn try to protect Charlotte when everyone learns she killed Wells. On the Ark, Abby risks getting floated in order to give Raven the chance to launch the escape pod.

Murphy returns to the camp carrying a horrific virus created by the Grounders to weaken the camp. After learning the Grounders plan to attack the next day, Bellamy, Finn and Raven come up with a plan to delay them.

Jasper and Bellamy go on a quest. Meanwhile, Clarke struggles to keep the peace after word of Jaha's discovery spreads.

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.

Raven faces an unexpected threat. Clarke must keep the peace among opposing factions in Sanctum.

While Bellamy tortures the Grounder, Raven and Clarke make contact with the Ark and ask Abby to help them save Finn. On the Ark, Kane deals with his guilt, and Jaha surprises the council with a shocking revelation.

Shumway secretly orders one of the 100 to kill Bellamy. Meanwhile, hallucinogenic nuts provide Octavia with an opportunity to help the Grounder escape the camp, and Bellamy and Clarke investigate a nearby underground depot, where they find military weapons.

The burden of leading weighs heavily upon Clarke and Bellamy when different challenges force them to determine who will live and die.