Young Cathy Blackthorn has never expereienced any looving response from her moth, it is her beloved Aunt Margatet who with a heart as big and warn as the summer sky, who has been more of a mother than her own could ever be. And when Cathy's father Frank Blackburn brings home a London street urchin and announces this will be the son he and Rita had never had. Cathy despairs of ever winning her partent's love. But Cathy is a generous soul, and tries to give the young lad a chance to prove himself - one way or the other- but unlike her best friend, David Leyton, something about him makes her more than uneasy.