Jemima, the unexpected and unwanted thirteenth child, is brought up in poverty by a drunken slattern of a mother, whilst her twin Sophie is taken to live nearby by a kind aunt. Jemima knows that spoilt Sophie doesn't like her. Because Jemima is the clever one. She loves school and wants to become a teacher. Jemima pursues her dream to begin her training. Meantime, she works at Baxters, the local outfitters, where she meets Richard, reluctant heir to the business. They become friends, both trapped in a life not of their choosing. Then Sophie comes to seek Jemima's help. Jemima faces a difficult dilemma. Must she now sacrifice everything for the sake of her twin?