Act 1:

In the forest of Fontainebleau, amidst a harsh winter, Don Carlos, the Prince of Asturias, meets Elisabeth of Valois. They fall in love instantly (“Io la vidi” / “Je l’ai vue”). Their happiness is short-lived as Elisabeth is informed that she must marry King Philip II of Spain, Carlos’s father, to seal a peace treaty between their countries. Though heartbroken, Elisabeth agrees to the marriage out of duty (“La pace mia smarrita” / “Ma première amie”).

Act 2:

In the cloister of the monastery of San Yuste, Carlos prays for solace. He is visited by his friend Rodrigo, the Marquis of Posa, who encourages him to support the oppressed people of Flanders. Rodrigo pledges to help Carlos in his quest for personal and political freedom (“Restate!” / “Ah, je meurs l’âme joyeuse”). At the palace in Madrid, King Philip and Elisabeth are seen in a strained relationship. Carlos confronts Elisabeth and declares his love for her, but she rebuffs him, reminding him of her loyalty to the king (“Perduta ho la pace” / “Dites-lui que je l’aime”).

Act 3:

During a public celebration and auto-da-fé in front of the cathedral of Valladolid, Carlos demands that King Philip grant freedom to the people of Flanders. Philip denies the request and orders Carlos’s arrest. In a heated exchange, Rodrigo steps in to defend Carlos, earning Philip’s trust. The act ends with the execution of heretics, underscoring the brutal power of the Inquisition (“Spuntato ecco il dì d’esultanza” / “L’infant Carlos, notre espérance”).

Act 4:

In King Philip’s study, the king laments his loveless marriage and seeks advice from the Grand Inquisitor, who insists that both Carlos and Rodrigo must die to maintain the power of the throne and the Church (“Ella giammai m’amò” / “Elle ne m’aime pas”). Rodrigo visits Carlos in prison, revealing his plan to sacrifice himself for his friend’s freedom (“Per me giunto è il dì supremo” / “Vous qui fléchissez”). As Rodrigo is killed by Philip’s guards, he hands Carlos a letter from Elisabeth, arranging a final meeting at the monastery.

Act 5:

In the monastery of San Yuste, Elisabeth prays for peace and strength (“Tu che le vanità” / “Toi qui sus le néant”). She meets Carlos and urges him to continue his fight for Flanders. Their farewell is interrupted by King Philip and the Grand Inquisitor, who come to arrest Carlos. As the confrontation reaches its peak, the ghost of Emperor Charles V appears, drawing Carlos into the cloister, symbolising his escape from earthly struggles and the oppressive forces around him. The opera ends with a powerful assertion of divine intervention and eternal peace.