When Bonaria adopts Maria, the unloved fourth child of a widow, she tries to shield the girl from the truth about her role as an angel of mercy. Moved by the pleas of a young man crippled in an accident, she breaks her golden rule of familial consent, and in the recriminations that follow, Maria rejects her and flees Sardinia for Turin. Adrift in the big city, Maria strives as ever to find love and acceptance, but her efforts are overshadowed by the creeping knowledge of a debt unpaid, of a duty and destiny that must one day be hers.