In the distant future, a population boom leads to shortages of food, water and shelter. The world-wide government passes a law on a one-child-per-family policy. During this difficult time, seven twin girls are born, hidden by their grandfather because their mother died in childbirth. Named after the days of the week, they are trained from childhood to act like one person to keep their secret from the people around them and the police who check everyone on every street corner. That's how the girls appear in public - each on a different day. But one day Monday goes missing.