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.But Liz and Derek, two strangers thrust together on their 21st birthdays, are about to discover that the idyllic paradise comes with a cost, one that Ascension have neglected to publicise. What began as a day of celebration will end in a whirlwind of conspiracies and revelations that threaten to upend the very foundations of Sallustria forever.