Ark City, a city-ship of mammoth proportions, holds constant vigil over the metropolis of Sallustria. This marvel of technology is the home of Ascension, an organisation who have successfully engineered a procedure that unlocks the full potential of the human brain. All Sallustrian citizens undergo mandatory testing at age 21 to determine their viability and, if they find themselves among the lucky few successful candidates, are permitted access to the floating utopia.