Act 1

Don Carlo, Infant of Spain, is thinking about Elizabeth whom he loves and had wanted to marry, but for reasons of state is now the wife of his father, King Philip II. Don Carlo confides his thoughts with Rodrigo, the Marquis of Posa, who urges him to devote his energies instead to defending the oppressed Flemish people.

Princess Eboli and other ladies-in-waiting are passing their time singing. Their joy ends when the Queen, Elizabeth arrives unable to hide her sorrow. Rodrigo convinces the queen to receive Don Carlo, who tells her how the Flemish are suffering, but his passion gets the better hand of him. Elizabeth tries to calm him down, but cannot hide her own love to him. Later, Rodrigo is in private audience with the king, he warns him to reign with less severity. Philip is impressed by Rodrigo’s sincerity, but is mainly concerned that there might be something between the queen and his son, and so asks Rodrigo to watch them carefully.

Act 2

Princess Eboli believes that Don Carlo is in love with her and so invites him to an evening teyst using an anonymous message. Don Carlo keeps the appointment, thinking that the message is from the queen. When Princess Eboli discovers the misunderstanding, her pride is wounded and so she plans revenge.

Don Carlo makes a stand for the freedom of the Flemish when a few convicts are sent to be burnt at the stake. Philip refuses to listen to his son. Don Carlo loses his temper with his father and draws his sword, but is quickly disarmed by Rodrigo.

Act 3

At night in his room, Philip is deep in thought: Elizabeth does not love him. If he decides to have Don Carlo killed, the Grand Inquisitor would be willing to pardon him. However, his son’s “crime” is a minor offence, compared to the bold aspirations of freedom for the Flemish expressed to Rodrigo: it is he who must die. Elizabeth arrives: someone has stolen her jewelry casket. The king has it and orders it to be opened: inside is a portrait of Don Carlo. Accused of adultery, the queen faints. Princess Eboli catches her, nut is herself in shock: she was responsible for handing the casket to the king. She confesses this to the queen who, horrified, orders her to leave the court.

Don Carlo is in prison. Rodrigo joins him, having finally understood that he is to be the victim. He is shot by an assassin and dies. Don Carlo is then freed by his father, but makes his contempt for the king public.

Act 4.

Don Carlo has decided to leave for Flanders. He bids a final farewell to Elizabeth in the cloister, but is surprised by the king, who orders the Grand Inquisitor to kill him. A monk appears from the shadows of the cloister at this point: it is Charles V, who grabs Don Carlo by the hand and, to the surprise of all, pulls him into the cloister.