It's been nearly 100 years since Earth was devastated by a nuclear apocalypse, with the only survivors being the inhabitants of 12 international space stations that were in orbit at the time. Three generations later, the survivors number 4,000 -- and resources are running out on their dying "Ark" (the 12 stations now linked together and repurposed to keep the survivors alive). Capital punishment and population control are the order of the day, as the leaders of the Ark take ruthless steps to ensure their future -- including secretly exiling a group of 100 juvenile prisoners to the Earth's surface to test whether it's habitable. No one has set foot on the planet in nearly a century -- until now. Among the exiles are Clarke, the teenage daughter of the Ark's chief medical officer; Wells, son of the Ark's Chancellor; the resourceful Finn; and brother/sister duo Bellamy and Octavia, whose illegal sibling status has them flaunting the rules. Technologically blind to what's happening on the planet below them, the Ark's leaders -- Clarke's widowed mother, Abby; the Chancellor, Jaha; and Jaha's shadowy second in command, Kane -- are faced with difficult decisions about life, death and the continued existence of the human race. For the 100 on Earth, however, the alien planet they've never known is a mysterious realm that can be magical one moment and lethal the next. With the survival of the human race entirely in their hands, the 100 must find a way to forge a new path on a wildly changed Earth that's primitive, intense and teeming with the unknown.