100 young exiles from a dying space station are sent to the planet Earth 97 years after a nuclear apocalypse to see if it's habitable.

After discovering that Jasper may still be alive, Clarke, Bellamy, Octavia, Finn and Monty set out to locate him and are shocked at what they find.

Clarke, Finn and Wells set out in search of an antibiotic to treat Jasper's wounds, when an acid fog forces them to seek shelter...and forgiveness for past crimes.

Abby risks having herself floated in order to give Raven the chance to stow-away in the escape pod bound for Earth.

After exposing Kane's plan to reduce the population of the Ark, Abby and Chancellor Jaha notice a signal from Earth and realize at least some of the 100 must still be alive.

While Bellamy leads his crew into Grounder territory in a search for Olivia, Raven can't help but notice the deep connection between Finn and Clarke.

While Clarke and Raven make contact with the Ark, Abby is removed from the council and Jaha reveals that there are not enough drop ships for everyone on the Ark.

While some of the 100 accidentally eat hallucinogenic nuts, Clarke and Bellamy go on a mission to find supplies for winter and are brought closer by a terrifying event.

All hell breaks loose when Clarke and Finn attempt to broker peace with the Grounders. And tragedy strikes during the Unity Day celebration on the Ark.

Murphy returns to camp claiming to have been held captive and tortured by the Grounders, and Clarke and Bellamy have very different opinions on how to handle his return.

With a low food supply at camp, Clarke and Finn lead a group out to hunt for food and wind up with Finn's life in danger. Meanwhile, Raven makes Bellamy an offer he can't refuse.

Those remaining on the Ark must come to terms with the inevitable. Meanwhile, Clarke and Finn find themselves facing a new enemy.

It's the end of the world as the conflict on the ground comes to a head and the situation on the Ark comes to a stunning conclusion.