Albert and Beauchamp rush to Monte Cristo’s house, but are told that he is not receiving any visitors. However, the servant at the door reveals that Monte Cristo will be attending the opera that evening. Albert sends word to Franz, Debray, and Maximilian to meet him at the opera. He then goes to see Mercédès and asks her whether she knows of any reason why Monte Cristo should consider Fernand his enemy. Mercédès tries to convince her son that Monte Cristo is not an enemy and begs him not to quarrel with a man he so recently considered his friend.
After Albert leaves Mercédès, she instructs a servant to follow him all night and report back to her about his activities. At the opera, Albert storms into Monte Cristo’s box, insults him, and challenges him to a duel. The duel is set for eight o’clock the following morning and is to be carried out with pistols. Monte Cristo asks Maximilian and his brother-in-law, Emmanuel, to act as seconds, or assistants, at the duel.
Mercédès pays a desperate visit to Monte Cristo. Monte Cristo explains to Mercédès why he hates Fernand, showing her the false accusation that Fernand personally mailed to the public prosecutor so many years before. Mercédès falls to her knees and begs his forgiveness, declaring her enduring love for Edmond Dantès. She pleads with Monte Cristo to save her son’s life, beseeching him to take vengeance only on those who are guilty. Monte Cristo’s vengeful will is broken, and he swears that Albert’s life will be saved. However, his dignity requires that he still fight the duel, which means that he himself must die the next day.
Monte Cristo confides to Maximilian and Emmanuel that he plans to let himself be killed. He then demonstrates his almost superhuman skill with the pistol so that there will be no doubt as to whether he lost the duel on purpose. Albert finally arrives at the site of the duel, but rather than pick up his pistol he apologizes to Monte Cristo, telling him that he was right to avenge Fernand for wronging him. Monte Cristo realizes that Mercédès has told her son the entire story.
Albert and Mercédès both plan to leave all their worldly possessions behind and create a new life away from the sins of Fernand. As they are about to depart their home forever, a letter from Monte Cristo arrives. Monte Cristo instructs Mercédès to travel to Marseilles, to the house in which Louis Dantès once lived. Buried under a tree in front of that house is the money that Dantès once planned to use to start a family with Mercédès. He writes that this money, though a pittance, is rightfully hers and should be enough to support her comfortably for the rest of her life. Mercédès accepts the gift and declares that she will use it as a dowry to gain entrance to a convent.
Monte Cristo comes home to Haydée, who has been eagerly awaiting him. He realizes that he might love Haydée as he once loved Mercédès. Just as they bask in each other’s company, Fernand bursts in, enraged that his son did not follow through on the duel. Fernand then challenges Monte Cristo to a duel himself. Before fighting, Fernand demands to know who Monte Cristo really is. Monte Cristo disappears momentarily and then returns in the clothes of a sailor. Recognizing him instantly as Edmond Dantès, Fernand is stricken with terror and flees the house. He returns home to find his wife and son departing forever. As they pull away from the house, Fernand shoots himself in the head.