The White Sister.

Angela Chiaromonte is the daughter of a wealthy Italian prince who is killed in a fall from his horse. Though Angela stands to inherit half of a large estate, her older half-sister burns the will and thus inherits everything herself, throwing Angela into poverty. Fortunately, Angela is engaged to marry dashing Captain Giovanni Severi - but he soon is captured by Arabs while on an expedition to Africa. Believing him dead, Angela, dedicating her life to his memory, becomes a nun, unaware that her lover has escaped his captors and is returning to Italy. The dramatic climax takes place against a backdrop of the eruption of Mount Vesuvius.