The action takes place in Spain in 1568, the thirteenth year of the reign of King Philip II. The basis of the plot is the history of the relationship between Philip II, his son Don Carlos, heir to the Spanish throne, and his wife – Queen Elizabeth.
In Aranjus, the residence of the Spanish king near Madrid, is the entire Spanish court. Here the son of the king is Don Carlos. The king is cold towards him, he is busy with public affairs and his young wife, who was formerly the fiancée of Don Carlos. To his son, Philip II put his servants on to spy on him.
In Arancus comes from Flanders the Marquis of Pose, a childhood friend of the prince, with whom he has touching memories. Infante opens to him in a criminal love for his stepmother, and the Marquis arranges Don Carlos meeting with Elizabeth alone. In response to the ardent love affidavits of the prince, she asks him to send his love to the unfortunate Spanish kingdom and passes him several letters with “tears of the Netherlands.”
After reading these letters, Don Carlos decides to ask his father to appoint him viceroy to the Netherlands, instead of the alleged brutal Duke of Alba. This intention is approved by the Marquis of Pose.
The court of the king moves to the royal palace in Madrid. With difficulty, Don Carlos is seeking an audience with Philip. He asks to send him to Flanders, where he promises to pacify the rebellion in Brabant. The king refuses, he believes that the place of the prince at the court, the Duke of Alba will go to Flanders.
Don Carlos is disappointed, at this time the page of the queen sends him a secretly love note asking to come on a date for half of Elizabeth. Prince is sure that the note from the queen, he comes to the specified place and meets there the maid of honor of Elizabeth, Princess Eboli. Infant in perplexity. Eboli explains to him in love, she seeks protection from his encroachments on his own innocence and in proof gives the prince a letter. Don Carlos hardly begins to understand his tragic mistake, the princess, seeing indifference to her, guesses that the signs of infanta attention, which she took on her account, actually belonged to the queen. Eboli drives the prince, but before that he asks her to give her the key, which gave Don Carlos a page, and a love letter to her of the king, which she had just given to the prince herself.
Meanwhile, at the court of the king, the prince has enemies who do not like the unbalanced character of the heir to the throne. The confessor of King Domingo and the Duke of Alba believe that such a monarch will be very uncomfortable on the Spanish throne. The only way to take Don Carlos away is to make the king believe in the Queen’s love for her son, in this case, according to Domingo, they have an ally – Princess Eboli, in whom Philip is in love.
Learning of the king’s refusal to send Prince to Flanders, Poza is upset. Don Carlos shows the friend a letter from the King to Princess Eboli. The Marquis warns the Infanta of the intrigues of the insulted princess, but at the same time shames him for wanting to use the stolen letter. The pose tears him and, in response to the misery of the unfortunate Infanta, promises to arrange again his meeting with the queen.
From the Duke of Alba, Domingo and Princess Eboli, Philip II learns about the “treachery” of Elizabeth, he loses peace and sleep, he sees conspiracies everywhere. In search of an honest man who would help him establish the truth, the King’s gaze stops at Marquis Pose.
Philip’s conversation with the marquis is most like a conversation between a blind man and a deaf person. Poza considers it his duty first of all to put in a word for his suffering Flanders, where people’s freedom is strangled. The old monarch cares only about personal well-being. Philip asks the marquis “to enter into the confidence of his son,” “to experience the heart of... the queen” and to prove his devotion to the throne. leaving, the noble grandfather still hopes that he will be able to achieve freedom for his homeland.
As envoy Philippe Pose gets a meeting alone with the queen. He asks Elizabeth to persuade Don Carlos to go to the Netherlands without the blessing of the king. He is sure that the royal son will be able to collect “rioters” under his banners, and then the father, after seeing the reconciled Flanders, will himself appoint her viceroy to this province. The Queen sympathizes with the patriotic plans of Marquis Pose and appoints Don Carlos a date.
The Marquis of Pose gives the king personal letters to Don Carlos. Among them, the monarch recognizes in a handwriting the note of Princess Eboli, who, wanting to prove the betrayal of Elizabeth by her husband, hacked the queen’s box and stole the letters of Don Carlos, written by Elizabeth, as it turned out, even before her marriage. Pose asks the king for a piece of paper with his signature, which would allow him to arrest an unbalanced prince, as a last resort. Philip gives such a document.
At court, the behavior of the Marquis of Pose is perplexing, which reaches the limit when the grandee orders to arrest Don Carlos on the basis of a letter from the king. At this time the director of the post, Don Raymond de Taxis, appears, he brings a letter to Pose, which is addressed to Prince Orange, who is in Brussels. It should explain everything to everyone.
Princess Eboli informs Elizabeth about the arrest of the Infanta and, tormented by the throes of conscience, confesses her villainy against the queen, she orders to send her to the monastery of St. Mary.
After meeting with the queen, on which he asks Elizabeth to remind the prince of their youthful oath, the Marquis of Pose goes to prison to his friend Don Carlos. Knowing that this is their last meeting, he reveals his plan to the infant. To save Carlos, he wrote a letter to Prince Orange of his imaginary love for the queen and that Infante Don Carlos was given to them by Philip only to divert his eyes. Pose sure that his letter will fall into the hands of the monarch. The prince is shocked, he is ready to run to his father-king to ask forgiveness for himself and the marquis, but it’s too late: a shot is being fired, the marquis Pose is falling and dying.
In prison, to release his son, Philip comes with grants. But instead of the grateful and humble Don Carlos, he finds there a grief-stricken man who accuses the king of the death of a friend. Around the prison, noise grows, this in Madrid begins a rebellion of the people, which requires the release of the prince.
At this time, in the hands of the spies Duke of Alba gets a monk, a Carthusian. He had letters from the Marquis of Pose to Flanders, which dealt with the escape of the Crown Prince to the Netherlands, where he would lead an uprising for the independence of this country. The Duke of Alba immediately sends the letters to the Spanish King.
King Philip calls for the Grand Inquisitor. He is tormented by the thought that infanticide is a grave sin, while he decided to get rid of his son. To appease his conscience, the old monarch wants to enlist the support of the church in his crime. The great inquisitor says that the church is able to forgive the suicide and cites the argument: “In the name of justice, the eternal son of God was crucified. * He is ready to take responsibility for the death of the Infanta, if only the throne of liberty was not the champion of freedom.
Night falls, Don Carlos comes on a date with Elizabeth. He goes to Flanders, determined to make friends in the name of friendship what they dreamed of with the Marquis. The Queen blesses him. The king appears with the Grand Inquisitor. The queen faints and dies, Philip without a shadow of a doubt passes his son into the hands of the Grand Inquisitor.