Young Cathy Blackthorn has never experienced any loving response from her mother; it is her beloved aunt Margaret, with a heart as big and warm as the summer sky, who has been more of a mother than her own could ever be. And when Cathy's father Frank Blackthorn brings home a London street urchin and announces this will be the son he and Rita have never had, Cathy despairs of ever winning her parents' love. Cathy is a generous soul, though, and tries to give the young lad a chance to prove himself, but unlike her best friend, David Leyton, something about him makes her more than uneasy.