"What if being normal was the difference between life and death?"
"Pure" takes place on a world far from Earth. Ages ago, a number of humans with special powers (not unlike the "mutants" of Marvel's X-Men), settled here to get away from the treatment they had gotten from mudanes. By now, so much time has passed almost everyone thinks this planet really is Earth.
The planet's enviroment is fairly harsh, mostly desert. The majority of the people live in city-states. Materially, the people live much like circia-2000 Earth, high technology banned to all but a few. The more powerful have formed rulling families, and how much power a person has generally determined his lot in life. Those who do not develop powers by 18, unless they have high IQs, are slated for euthinization, branded as substandard or "subbers." The official reason is to keep them from weakening the gene pool. At one time they were simply kept from reproducing, but it was changed to euthanasia on the grounds the "subbers" were living a poor existance.
Some are able to fool the system by getting bionic implants in the black market. But this is highly illegal as although the person now has powers, the "bad genes" are still there and the person could contaminate the gene pool. Those caught with implants are tortured to death rather than simply put to sleep in order to serve an example. As Executioners, enforcers of this policy, will try to track down those who do not turn themselves in when their time is up, the only other option for a "subber" other than bionics or death is to try to flee the city.
Outside the city-states in the desert, life is harsh, brutish, and often short. Wild creatures, including vampire-like beings, are a potential end for those wandering about. There are a few small communities where normals are able to eke out a living, but they are invariably ruled by someone with special powers. Any youngster they find developing powers is usually killed.