It has been 118 years since Earth was ravaged by nuclear war. The population was wiped out completely, besides a few lucky survivors who escaped onto the ten space crafts that ten individual nations had active at the time. They merged and created The Continent; one huge craft built to hold the remainder of the population until Earth was once again able to sustain life. Ideally, The Continent should have lasted up to 250 years, up to eight generations, but the oxygen levels are rapidly falling and the Council is calling for a culling if there is no other way to save them; killing off a huge chunk of the population is the only way to save the rest of them.
In an effort to stop this, some council members suggested sending people down to earth, to try and discover if the environment is able to hold life of any form. If it is, humans can return to earth and start rebuilding. If not, either the culling will happen, or the human race will die. Who, you might ask, is expendable enough that they can be sent to earth, may they live or die? Criminals.
All criminals on The Continent are 21 or younger, since anyone older than that isn’t worth wasting oxygen on once they’ve committed a crime and is ‘floated’ – sent out into space to die. Some of the delinquents are murderers, some stole fruit. Any and all crimes are considered extreme offences when people are struggling to survive.
Individualism doesn’t do well on The Continent, which has some very strict laws.