It is well known that Philip II supplanted his unfortunate son Don Carlos, and married the princess to whom the youth had been betrothed with the consent of both crowns. Our poet depicts the disastrous attachment of the devoted pair. The piece opens with a passionate soliloquy of Isabella, in which she reproaches herself bitterly for the unconquered love she bears to the son of her husband. Her mind revolts at the idea of such an affection, which she fears her indiscretion may one day betray to its object. She distrusts her every word and look. In the midst of this, the prince enters, evidently unhappy, and earnestly asks her reason for avoiding his presence. He perceives that the whole court is hostile to him; miserable and oppressed, he cannot wonder that he reads envy and hatred in every countenance about him, since he is conscious that he does not possess the favor of his father and sovereign. From the queen, however, “born under a milder sky,” whose nature is all gentleness, he expected pity. Isabella is moved to the expression of sorrow for his misfortunes; his joy in her sympathy is extreme, and in return he offers condolence with her for her “hard lot,” which she repels with some confusion; immediately after, hinting at the relation in which she stands to him, she offers to intercede with the king in his behalf. Carlos declines this offer, telling her she is the innocent cause of all his sufferings, and reminds her of their former affection and engagement; bitterly alluding to his father's hatred, and the greatest wrong he has inflicted, in depriving him of his bride. Isabella reproves his resentment against the king, whom she imagines deceived by false counsellors, and refuses to listen to his passionate complaints; the prince pleads with her to remain, and at length bids her renounce and accuse him. Now comes the discovery. When Carlos calls himself guilty, the queen says, “Art thou alone the guilty?” This thoughtless exclamation betrays to the prince the state of her heart; and shocked at her own indiscretion Isabella implores him to leave her. He pleads that flight would not protect him from the vengeance of Philip, who regards him with detestation, though ignorant of his only fault. The queen departs, forbidding him to follow her, and Perez enters. This person, a warm friend to the prince, attempts to console his evident wretchedness, which he attributes to his father's displeasure, by assuring him that the king has been wrought upon by false rumors and the machinations of his enemies. His offers of service and devoted attachment affect Carlos, who nevertheless will not reveal the secret cause of his grief. He yields, however, to the entreaties of Perez, to accept him as his friend, and permit him to share his destiny; congratulating himself even in the midst of wretchedness that he is less worthy of compassion than Philip on his throne.