When their father runs off with the tobacconist's wife, Isobel and Caro are left to the far from tender mercies of their mother, Iris, who relieves her frustration with bouts of fury towards her elder daughter, Isobel. Bewildered and hurt by their mother's lack of affection, the girls turn inwards for support, erecting a fence of fierce mutual loyalty against the outside world.

Dispatched to a convent school, the sisters find the discipline harsh but they discover, too, a love and security lacking at home . . . until the arrival of cousin Ursula. Ursula perpetrates sly tricks - masked by a deceptively innocent air. Pushed to the limit, Isobel decides to exact her own revenge . . .