In the series premiere, 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.

Having discovered that Jasper may still be alive Clarke Bellamy Octavia Finn and Monty set out on a mission to locate their friend and are shocked at what they find. Meanwhile on the Ark Abby is determined to get to Earth and enlists Raven (guest star LINDSEY MORGAN) to craft an escape pod.

In a desperate attempt to treat Jasper's festering wounds Clarke Finn and Wells (ELI GOREE) set out in search of a seaweed antibiotic. Bellamy and his crew go hunting for food and are joined by Charlotte (guest star IZABELA VIDOVIC) a lovable 13-year-old who feels safe under Bellamy's protection. A thick acidic fog appears forcing Clarke Finn and Wells to seek shelter inside an ancient van. While they are trapped Clarke confronts Wells on his betrayal that resulted in her father's death.

After the shocking death of one of their own, Clarke and Finn grow closer as they try to figure out a way to communicate with the Ark. Bellamy must keep the group from turning on one another as life on Earth takes a desperate turn. Meanwhile, Abby risks having herself floated in order to give Raven (recurring guest star LINDSEY MORGAN) the chance to stow-away in the escape pod bound for Earth.

Clarke's newfound romance with Finn is threatened. After suffering a blow to the head, Octavia wakes up to find a Grounder watching her. On the Ark, Abby exposes Kane's plan to reduce the population of the Ark. Then, Chancellor Jaha and Abby notice a signal and realize at least some of the 100 must still be alive on Earth.

Bellamy leads his crew into Grounder territory as they search for Octavia. Raven can't help but notice the deep connection between Finn and Clarke. Meanwhile, flashbacks reveal Bellamy and Octavia's difficult childhood on the Ark.