From the introduction:
For the drow, power is not earned through trial and hardship. Power is a birthright. But even among the drow, power is a hierarchical beast. Those born into the upper class of drow society possess not only the material excess and social influence that characterizes aristocracy across most races, but also a suit of physical and magical powers that far exceeds that of ordinary drow. Using these powers as a sign of divine favor or a cosmic mandate to rule over others with both iron fist and cruel intent, drow nobles lord over both the lesser races and their poorly endowed kin, commanding drow society both from the shadows and in plain view. In effect, there is a glass ceiling for most drow in their society, a point of no return where a drow can no longer hope to amass the dark power that she craves, a limit not in personal power or ambition, but in birth.