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The 100

Ever since a devastating nuclear war, humanity has lived on spaceships far above Earth's radioactive surface. Now, one hundred juvenile delinquents - considered expendable by society - are being sent on a dangerous mission: to re-colonize the planet. It could be their second chance at life...or it could be a suicide mission.
CLARKE was arrested for treason, though she's haunted by the memory of what she really did. WELLS, the chancellor's son, came to Earth for the girl he loves - but will she ever forgive him? Reckless BELLAMY fought his way onto the transport pod to protect his sister, the other half of the only siblings in the universe. And GLASS managed to escape back onto the ship, only to find that life there is just as dangerous as she feared it would be on Earth.
Confronted with a savage land and haunted by secrets from their pasts, the hundred must fight to survive. They were never meant to be heroes, but they may be mankind's last hope. (Sony Reader Store)
In every chapter the reader learns more secrets about the past of the four protagonists. Glass' secret is obvious, Wells' not so much, and his is a dark one. I didn't like him anyway. It is his fault that Clarke's parents were being executed.
It is 300 years after the nuclear war and the Colony, the spaceship, wasn't build to last this long. It runs out of air. Since Glass stayed on the ship and even got a pardon, you see what is going on there and how people live in space. Society hasn't changed much. The rich still despise the poor, the poor despice the rich, the rich have much more privileges (like running water 24/7).
The kids on the ground have to learn how to survive, since they only have rations for a month. They have to build some kind of society of their own. They also have to learn how to defend themselves, because they are not the only living things on earth.
Now I just have to wait for the second book, that is going to come out in September.