[This synopsis is based on the original five-act version composed for Paris and completed in 1866. Important changes for subsequent versions are noted in indented brackets. First lines of arias, etc., are given in French and Italian].
[This act was omitted in the 1883 revision.]
The Forest of Fontainebleau, France in winter
A prelude and chorus of woodcutters and their wives is heard. They complain of their hard life, made worse by war with Spain. Elisabeth, daughter of the King of France, arrives with her attendants. She reassures the people that her impending marriage to Don Carlos, Infante and son of Philip II, King of Spain, will bring the war to an end, and departs.
[This was cut before the Paris premiиre and replaced by a short scene in which Elisabeth crosses the stage and hands out money to the woodcutters.]
Carlos, coming out from hiding, has seen Elisabeth and fallen in love with her (Aria: "Je l'ai vue" / "Io la vidi"). When she reappears, he initially pretends to be a member of the Count of Lerma's delegation. She asks him about Don Carlos, whom she has not yet met. Before long, Carlos reveals his true identity and his feelings, which she reciprocates (Duet: "De quels transports poignants et doux" / "Di quale amor, di quanto ardor"). A cannon-shot signifies that peace has been declared between Spain and France. Thibault appears and gives Elisabeth the surprising news that her hand is to be claimed not by Carlos but by his father, Philip. When Lerma and his followers confirm this, Elisabeth is devastated but feels bound to accept, in order to consolidate the peace. She departs for Spain, leaving Carlos equally devastated.
[This act is act 1 in the 1883 revision.]
Scene 1: The monastery of Saint-Just (San Jerуnimo de Yuste) in Spain
The scene takes place some time after Philip II and Elisabeth are married. Monks pray for the soul of the former Emperor Charles V ("Carlo Quinto"). His grandson Don Carlos enters, anguished that the woman he loves is now his stepmother.
[In the 1883 revision, he sings a revised version of the aria "Je l'ai vue" / "Io la vidi", which was salvaged from the omitted first act but with some different music and different text to reflect his current situation of already knowing he can't marry Elisabeth whereas in the original he was still supposed to marry her when he sings the aria.]
A monk resembling Carlo Quinto offers him eventual consolation of peace through God, an early herald of one of the opera's themes. Carlos greets his great friend Rodrigue, Marquis of Posa, who has just arrived from the oppressed land of Flanders (Aria: "J'йtais en Flandres").
[This was cut during the pre-premiиre rehearsals.]
Posa asks for the Infante's aid on behalf of the suffering people there. Carlos reveals that he loves his stepmother. Posa is sympathetic but encourages him to leave Spain and go to Flanders. The two men swear eternal friendship (Duet: "Dieu, tu semas dans nos вmes" / "Dio, che nell'alma infondere"). King Philip and his new wife, with their attendants, enter also to do homage at Charles V's tomb, while Don Carlos laments his lost love.
Scene 2: A garden near Saint-Just
Princess Eboli sings the Veil Song ("Au palais des fйes" / "Nel giardin del bello") about a Moorish King and an alluring veiled beauty that turned out to be his neglected wife. Elisabeth enters. Posa gives her a letter from France together, secretly, with a note from Don Carlos. At his urging (Aria: "L'Infant Carlos, notre espйrance" / "Carlo ch'и sol il nostro amore"), Elisabeth agrees to see the Infante alone. Unaware of this relationship, Eboli infers that she, Eboli, is the one Don Carlos loves.
When they are alone, Don Carlos tells Elisabeth that he is miserable, and asks her to request Philip to send him to Flanders. She promptly agrees, provoking Carlos to renew his declarations of love, which she piously rejects. Don Carlos exits in a frenzy, shouting that he must be under a curse. The King enters and becomes angry because the Queen is alone and unattended. He orders the lady-in-waiting who was meant to be attending her, the Countess of Aremberg, to return to France, prompting Elizabeth to sing a sorrowful goodbye-aria. (Aria: "Oh ma chиre compagne" / "Non pianger, mia compagna"). The King approaches Posa, with whose character and activism he is impressed, intent on rewarding him. Posa begs the King to stop oppressing the people of Flanders. The King calls Posa's idealism unrealistic and warns that the Grand Inquisitor is watching him; Philip nevertheless asks if he can grant Posa another request.
[This dialogue was revised three times by Verdi.]
[This act is act 2 in the 1883 revision.]
Scene 1: Evening in the Queen's garden in Madrid
Elisabeth is tired, and wishes to concentrate on the following day's coronation of the King. To avoid the divertissement planned for the evening, she exchanges masks with Eboli, assuming that thereby her absence will not be noticed, and leaves.
[This scene was omitted from the 1883 revision.]
[The ballet (choreographed by Lucien Petipa and entitled "La Pйrйgrina") took place at this point in the premiиre.]
Don Carlos enters, clutching a note suggesting a tryst in the gardens. Although he thinks this is from Elisabeth, it is really from Eboli, to whom he mistakenly declares his love. When Eboli discloses her identity and that she now knows his secret - that he was expecting the Queen - Carlos is horrified. When Posa enters, she threatens to tell the King that Elisabeth and Carlos are lovers. Eboli only just escapes from being stabbed by Posa, on Carlos intervention, and exits in a vengeful rage. Just in case, Posa asks Carlos to entrust to him any sensitive political documents that he may have and, when Carlos agrees, they reaffirm their friendship.
Scene 2: In front of the Cathedral of Valladolid
Preparations are being made for an "Auto-da-fй", the public parade and burning of condemned heretics. While the people celebrate, monks drag the condemned to the woodpile. A royal procession follows, with the King addressing the populace. Don Carlos interrupts it by bringing forward six Flemish deputies, who plead with the King for their country's freedom. Although the people and the court are sympathetic, the King, supported by the monks, orders the deputies' arrest. Carlos draws his sword against the King. The King calls for help but the guards will not attack Don Carlos. Posa steps in and persuades Carlos to surrender his sword. The King uses it to dub Posa Duke, the woodpile is fired and, as the flames start to rise, a heavenly voice can be heard promising peace to the condemned souls.
[This act is act 3 in the 1883 revision.]
Scene 1: Dawn in King Philip's study in Madrid
Alone, the King, in a reverie, laments that Elisabeth has never loved him, that his position means that he has to be eternally vigilant and – returning to a central theme – that he will only sleep properly when he is in his tomb in the Escorial (Aria: "Elle ne m'aime pas" / "Ella giammai m'amт"). The blind, ninety-year-old Grand Inquisitor is announced and shuffles into Philip's apartment. When the King asks if the Church will object to him putting his own son to death, the Inquisitor replies that the King will be in good company: God sacrificed His own son. The King questions such an extreme approach. However, undaunted, the Inquisitor demands that the King have Posa killed. The King refuses to kill his friend, whom he admires and likes, objecting to such wanton cruelty. However, the old monk reminds Philip that the Inquisition can take down any king; he has created and destroyed other rulers before. This moment highlights the symbiotic relationship between Church and State. Somewhat taken aback, the King suggests the Grand Inquisitor forget about the whole discussion. The latter replies "Forse!" – perhaps! – and leaves. In a moment of continuing high drama, Elisabeth enters, alarmed at the apparent theft of her jewel casket. However, the King produces it and points to the portrait of Don Carlos which it contains, accusing her of adultery. She protests her innocence but, when the King threatens her, she faints. In response to his calls for help, into the chamber come Eboli and Posa. Their laments of suspicion ("Maudit soit le soupзon infвme" / "Ah, sii maledetto, sospetto fatale"), cause the King to realise that he has wronged his wife. Posa then resolves to save Carlos, though it may mean his own death. Eboli feels remorse for betraying Elisabeth; the latter, recovering, expresses her despair.
[This quartet was revised by Verdi in 1883.]
Elisabeth and Eboli are left together.
[A duet, "J'ai tout compris", was cut before the premiиre.]
Eboli confesses not only that she stole the casket because she loved Carlos and he rejected her but also that, even worse, she has been the King's mistress. Elisabeth takes this in her stride and tells Eboli that she must go into exile or enter a convent. After she exits, Eboli curses the fatal pride that her beauty has bestowed on her, chooses the convent over exile and resolves to try and save Carlos from the Inquisition (Aria: "O don fatal" / "O don fatale").
Scene 2: A prison
Don Carlos has been imprisoned. Posa arrives to tell him that he will be saved but that he himself will have to die, incriminated by the politically sensitive documents which he had asked Carlos to entrust to him (Aria, part 1: "C'est mon jour suprиme" / "Per me giunto и il di supremo"). A shadowy figure appears and shoots Posa in the chest. As he dies, Posa tells Carlos that Elisabeth will meet him at Saint-Just the following day. He adds that he is content to die if his friend can save Flanders and rule over a happier Spain (Aria, part 2: "Ah, je meurs, l'вme joyeuse" / "Io morrт, ma lieto in core"). At that moment, Philip enters, offering his son freedom. Carlos repulses him for having murdered Posa. The King has not noticed that Posa is dead and cries out in sorrow.
[A duet included at this point for Carlos and the King was cut before the premiиre. The music was later re-used by Verdi for the Lacrimosa in his Requiem.]
Bells ring as Elisabeth, Eboli and the Grand Inquisitor arrive, while a crowd threatens the King, demanding the release of Carlos. In the confusion, Eboli escapes with Carlos. Although the people are brave enough with the King, they are terrified by the Grand Inquisitor, instantly submitting to his angry command to quieten down and pay homage to Philip.
[After the premiиre, some productions ended this act with the death of Posa; however, in 1883 Verdi provided a much shortened version of the insurrection, as he felt that otherwise it would not be clear how Eboli had fulfilled her promise to rescue Carlos]
[This act is act 4 in the 1883 revision.]
The moonlit monastery of Yuste
Elisabeth kneels before the tomb of Charles V. She is committed to help Don Carlos on his way to fulfil his destiny in Flanders, but she herself longs only for death (Aria: "Toi qui sus le nйant" / "Tu che le vanitа"). Carlos appears and they say a final farewell, promising to meet again in Heaven (Duet: "Au revoir dans un monde oщ la vie est meilleure" / "Ma lassщ ci vedremo in un mondo migliore").
[This duet was twice revised by Verdi.]
Philip and the Grand Inquisitor enter. The King has submitted to the church's domination and declares that there will be a double sacrifice: Posa and Carlos. The Inquisitor confirms that the Inquisition will do its duty. A short summary trial follows, confirming Carlos's putative culpability.
[The trial was omitted in 1883.]
Carlos, calling on God, draws his sword to defend himself against the Inquisitor's guards, when the old Monk suddenly emerges from the tomb of Charles V. He grabs Carlos by the shoulder, proclaiming that the turbulence of the world persists even in the Church; once again, we cannot rest except in Heaven. Philip and the Inquisitor recognize the Monk's voice as that of the King's father, former Emperor Carlo V. Everyone screams in shock and terror, whilst the Monk/former Emperor drags Carlos forcibly into the tomb and closes the entrance. The curtain falls.