Girl who lived Underground

In 2493 there are two very different civilizations surviving in a world so damaged no-one can go outside in daylight. The Thrallians are a high tech civilization, unaware of the existence of the Centrals, who live in a deserted subway. That is until Derek and Patric discover a girl locked in the Supers' quarter. A girl with blonde hair and blue eyes, unlike anyone in Thrallia.