We learn the nature of the heroine’s hastily formed plan at the beginning of the second act, in which she visits her brother in his cell, with the object of discovering whether he is worthy of rescue.  She reveals Friedrich’s shameful proposal to him, and asks if he would wish to save his life at the price of his sister’s dishonour.  Then follow Claudio’s fury and fervent declaration of his readiness to die; whereupon, bidding farewell to his sister, at least for this life, he makes her the bearer of the most tender messages to the dear girl whom he leaves behind.  After this, sinking into a softer mood, the unhappy man declines from a state of melancholy to one of weakness.  Isabella, who had already determined to inform him of his rescue, hesitates in dismay when she sees him fall in this way from the heights of noble enthusiasm to a muttered confession of a love of life still as strong as ever, and even to a stammering query as to whether the suggested price of his salvation is altogether impossible.  Disgusted, she springs to her feet, thrusts the unworthy man from her, and declares that to the shame of his death he has further added her most hearty contempt.  After having handed him over again to his gaoler, her mood once more changes swiftly to one of wanton gaiety.  True, she resolves to punish the waverer by leaving him for a time in uncertainty as to his fate; but stands firm by her resolve to rid the world of the abominable seducer who dared to dictate laws to his fellow-men.  She tells Marianne that she must take her place at the nocturnal rendezvous, at which Friedrich so treacherously expected to meet her (Isabella), and sends Friedrich an invitation to this meeting.  In order to entangle the latter even more deeply in ruin, she stipulates that he must come disguised and masked, and fixes the rendezvous in one of those pleasure resorts which he has just suppressed.  To the madcap Luzio, whom she also desires to punish for his saucy suggestion to a novice, she relates the story of Friedrich’s proposal, and her pretended intention of complying, from sheer necessity, with his desires.  This she does in a fashion so incomprehensively light-hearted that the otherwise frivolous man, first dumb with amazement, ultimately yields to a fit of desperate rage.  He swears that, even if the noble maiden herself can endure such shame, he will himself strive by every means in his power to avert it, and would prefer to set all Palermo on fire and in tumult rather than allow such a thing to happen.  And, indeed, he arranges things in such a manner that on the appointed evening all his friends and acquaintances assemble at the end of the Corso, as though for the opening of the prohibited carnival procession.  At nightfall, as things are beginning to grow wild and merry, Luzio appears, and sings an extravagant carnival song, with the refrain: 

    Who joins us not in frolic jest
    Shall have a dagger in his breast;