The scene is set in the legendary kingdom of Allemonde.

Scene 1: A forest. Having lost his way, Golaud is wandering through a deep forest. He finds a young girl, weeping at the edge of a stream. She is frightened and will tell him nothing. He tells her he is the grandson of Arkel, King of Allemonde, and warns her of the dangers of the forest. She agrees to follow him; her name is Mélisande.

Scene 2: A room in the castle. Six months have passed. Golaud has married Mélisande and has written to his half-brother Pelléas of his fears that Arkel will not approve of the marriage. Geneviève, their mother, reads the letter to Arkel, who, although he does not understand Golaud’s action, will welcome them. Pelléas enters and asks to be allowed to go to the deathbed of his friend Marcellus. Arkel advises him to stay to attend his father, who is also near death.

Scene 3: Outside the castle. Geneviève, Mélisande, and Pelléas meet on the ramparts overlooking the sea. A storm comes up as they watch the ship depart.

Scene 4: A well in the park. Pelléas takes Mélisande to his favorite spot – an abandoned well where he goes to be alone. Playing over the water, Mélisande drops her wedding ring into the well.

Scene 5: A room in the castle. Golaud has been injured while riding. As Mélisande nurses him, she begins to weep, saying that she is unhappy but does not know why. Golaud sees that her ring is gone, and when she says that she lost it in the grotto by the sea he demands that she and Pelléas go immediately to find it.

Scene 6: Outside a grotto. Pelléas takes Mélisande to the grotto. The clouds part, and moonlight fills the beautiful grotto, revealing three starving beggars. Frightened, they return to the castle.

Scene I: One of the castle towers. Mélisande is at her window, singing and combing her hair. Pelléas, passing below, reaches for her hand, and as she leans forward her hair falls over the edge and envelops him. Golaud appears, telling them to stop their games.

Scene 2: The castle vaults. Golaud takes Pelléas beneath the castle to show him the ancient vaults. Pelléas is terrified by the darkness and the foul air.

Scene 3: A terrace outside the vaults. Emerging into the sunlight, Pelléas sees his mother and Mélisande on a terrace of the castle. Going toward them, he is stopped by Golaud, who warns him against his childish behavior with Mélisande: she is pregnant and must be treated carefully.

Scene 4: Outside the castle. Golaud and his son Yniold are on the terrace beneath Mélisande’s window. Golaud is torn with doubts and questions the boy about Pelléas and Mélisande. He puts him to the window to watch them, and he sees them staring endlessly at the light, never closing their eyes. The child is frightened and begs to be let down.

Scene I: A room in the castle. Pelléas tells Mélisande that, as his father has recovered, he plans to leave – but must see her once more at the fountain before going. Arkel enters, expressing his hopes for Mélisande’s happiness. Golaud comes in search of his sword and loses control, denouncing Mélisande as a false innocent, catching her by the hair and beating her.

Scene 2: A well in the park. Yniold, playing in the park, struggles to lift a large rock under which he has lost a toy. He gives up and runs off to the castle. Pelléas arrives first at the well, simultaneously wanting and not wanting to leave. Mélisande arrives breathless, having left Golaud asleep. Suddenly the noise of the closing of the castle gates is heard, and they realize that they will be discovered. They declare their love for each other, and, as they embrace, Golaud falls upon them, killing Pelléas and pursuing Mélisande through the woods.

Scene 3: A bedchamber in the castle. Mélisande, wounded, has borne a daughter and is dying. Golaud is overcome by what he has done, but is still ridden with doubt. He asks if she loved Pelléas, and she answers that she did – but that it was not a guilty love. She dies as the sun sets. Arkel tells Golaud that he must live, and so give her child the chance to live.