Sancho IV, king of Castile, is delighted with his welcome to Seville, and he is especially charmed by a black-haired beauty he catches sight of on a balcony. The alcaldes of the city identify her as Estrella Tabera, the Star of Seville. King Sancho whispers orders to his confidant, Arias, telling him to arrange for the monarch to visit Estrella the next evening. He also sends for Estrella’s brother, Don Bustos Tabera, in the hope of winning his agreement to the royal suit.

When Don Bustos is offered the command of the military post at Archidona, already sought by two veteran soldiers, the nobleman amazes the king by refusing the honor and by accepting with obvious reluctance other friendly gestures; his excuse is that he does not deserve them. At home, Don Bustos finds his sister and Don Sancho Ortiz planning their marriage. Before long the disguised king appears, but Don Bustos, pleading a house in disorder and foreseeing the possibility of a scandal, does not invite him in. Arias does succeed in entering the house, however. When he reveals his errand, Estrella indignantly refuses his request that she be kind to the king. Arias has better luck when he tries to bribe Matilde, the maid, who promises to admit the king to the house after dark.

That night, after the king has been admitted, Don Bustos returns home unexpectedly and finds the monarch there. Pretending not to believe that the intruder is the king, since a noble and just ruler would not stoop to dishonor, Don Bustos insults him as a masquerader. The angry king, with no legal way to get revenge for the insults he has endured, sends for Don Sancho Ortiz and offers to arrange the young nobleman’s marriage to anyone he chooses, in return for ridding the king of an enemy. Don Sancho is given a paper on which is written the name of the man he is supposed to kill.

In the meantime, Don Bustos, having forced Matilde to confess her treachery, hangs her from the king’s balcony. Then he instructs Estrella to arrange for her marriage to Don Sancho at once, and she sends her lover a message informing him of the plan and asking him to come to her. Don Sancho is faced with a conflict between duty and inclination. He loves Estrella, but he has sworn to serve the king faithfully; thus, when he meets Don Bustos, he picks a quarrel with his sweetheart’s brother and kills him in a duel. Afterward he stubbornly refuses to give any explanation of his deed and is taken, under arrest, to the Triana prison.

Estrella, awaiting the arrival of Don Sancho, receives instead the body of her dead brother. When she learns the name of his killer, she decides to go at once to the king to demand vengeance. Before her arrival at the palace, the king has already been assured that Don Sancho is loyally keeping silent about the king’s part in the death of Don Bustos. Since justice is expected, however, the king is forced to order the execution of Don Sancho. Speaking to Arias, the king marvels at the honor and dignity of the citizens of Seville.

When Estrella appears, the king delegates to her the power to pass sentence on the murderer of her brother and sends her, with his ring, to the Triana prison. Alone, he soliloquizes on the tragic results of his unbridled passion. Meanwhile, in the prison, loyal Clarindo is trying to amuse Don Sancho, who seems to be out of his mind. The alcaldes cannot understand his...