Tired of poverty, Keiko leaves home and soon takes a lover, but leads a wanton life without paying heed to his advice. However, the younger sister Yoshiko, is an innocent and kind girl. One day, with the sudden death of their mother in a car accident, Keiko learns that she and Yoshiko are actually stepsisters, and that she is the daughter of a murderer. She now plans extortion from Yoshiko's true father who is the president of a well-known trading company.