Clara, widow duchess of Santauro, has confined her daughter Margarita, of great beauty, in the Royal Boarding School, where she goes to take her out and to make her debut already. So that it does not affect the reputation of her daughter, she breaks off her affair with Luis de Castro, a “don Juan of today”, blackmailer and a drunkard. The duchess decides to celebrate a party, where Luis meets Margarita and seduces her. Clara receives Luis at home in order to ask him for her letters. Margarita, who sees him arriving, thinks he is coming to ask for her hand to her mother, and hidden listens the conversation. Such is the disillusion that Margarita falls ill and goes mad.