- Time:
- Place: Toledo, on the banks of the Tagus River, near Don Alonso's camp.
Don Alfonso, the king of Portugal, has declared war on Spain; because the Spanish queen Caritea has refused his offer of marriage, he has decided to take the country by force. The Portuguese are laying siege to Toledo. Diego, a Spaniard who is in love with Caritea, arrives at the Portuguese camp, where he asks for entry. He had fled Spain ten years earlier because he had been rejected by the queen and killed another of the queen's suitors, Pompey. Caritea, who had been in love with Pompey, promised to marry anyone who would deliver her Diego's head.
Caritea enters the Portuguese camp, disguised as a man. She has been trying to infiltrate the camp, but is nearly caught and killed, if it were not for Diego. Diego recognizes Caritea, and is still terribly in love with her. Caritea, however, does not recognize Diego, since it has been ten years since his escape.
Don Alfonso then arrives, and frees Don Fernando, Diego's elderly father, who has fallen prisoner. Alfonso is then informed that Caritea has been spotted, disguised, near the camp, and Alfonso explodes with fury.
Diego offers to take Caritea back to Toledo. He senses that Caritea is falling in love with him, so he proposes marriage to her. Caritea, however, reminds him that she has decreed only to marry the man who brings her the head of Don Diego. Fernando, knowing that his son is that same Diego who Caritea has vowed to have killed, fears for his son's life.
Don Alfonso, in his fury, challenges Diego to a duel, but is killed. Diego returns to Toledo the champion and praised by the people. Because he managed to kill the enemy of Spain, Don Diego can now reveal his true identity to Caritea. Caritea forgives him and agrees to marry him.
