By Day and by Night

In a world where over-population is out-of-control, the government decides to divide the population by implanting an enzyme into people's DNA to make them only active in either day or night, thereby splitting the society contained within its cloistered utopian/dystopian environs. Within this world, Aurora has lost her daughter and Urbane, a scientist finds an unknown child - but from which part of society ? (sci-fi-london)