100 young criminals that have been living in space on The Arch have been sent to Earth to test if it has become inhabitable after 97 years of being abandoned after a nuclear war.
S01E02 - Earth Skills
A search-and-rescue mission ends in surprise. Meanwhile, Raven helps Abby craft an escape pod.
S01E03 - Earth Kills
An antibiotic is sought to treat Jasper's wounds. Meanwhile, Bellamy and his crew hunt for food.
S01E04 - Murphy's Law
Clarke and Finn grow closer as they try to communicate with the Ark. Meanwhile, Bellamy maintains order within the group.
S01E05 - Twilight's Last Gleaming
Finn and Clarke's new relationship becomes a little more complicated. Octavia is knocked out and abducted by a Grounder.
S01E06 - His Sister's Keeper
Bellamy and his crew search for Octavia. Meanwhile, Raven notices a connection between Finn and Clarke.
S01E07 - Contents Under Pressure
Clarke finally makes contact with the arch and Bellamy brings a grounder to the camp to try to get some answers.
S01E08 - Day Trip
Clarke and Bellamy search for supplies as winter nears. Meanwhile, Octavia helps a friend escape.
S01E09 - Unity Day
Both the Ark and the 100 celebrate Unity Day. The Ark is devastated by first an explosion, then an attempted coup. Meanwhile, on the ground, Clarke, Finn, and Octavia set up a meeting with the grounders.
S01E10 - I Am Become Death
After one of the 100 return to camp with a virus, getting many of them sick, Octavia, Finn, Jasper, and Raven devise a plot to try to hold off the grounders from war.
S01E11 - The Calm
After losing nearly all food supplies through a fire, the remaining "100" are forced to go hunting despite the constant threat of the Grounders. Clarke and Finn are caught up in the aftermath of bombing the bridge and may have to pay a high price ... Meanwhile on the Ark: Councillor Kane goes to great lengths to find and save survivors in the repercussion of major destruction.
S01E12 - We Are Grounders, Part 1
Part 1 of 2. Clarke and Finn face a new enemy. Meanwhile, Bellamy saves Jasper
S01E13 - We Are Grounders, Part 2
Conclusion. Bellamy forces Octavia to make a difficult decision in the Season 1 finale. Later, Finn takes a risk.