Act 1
A forest. Golaud, grandson of Arkel, king of Allemonde, has lost his way whilst following the trail of a wild boar. His hounds have disappeared. Wandering amidst the trees, he hears the cries of a child: a little girl. He approaches and discovers a young woman, whose beauty and innocence overwhelm him. At her feet, in the waters of a fountain, he sees a crown and suggests retrieving it for her. But she protests strongly, then refuses to answer his questions, giving him only her name: Mélisande. Night falls and it grows cold. Mélisande agrees to follow Golaud. On the Allemonde castle promontory, Geneviève reads Arkel a letter that Golaud has written to his half-brother, Pelléas. Six months have passed.

Golaud relates his marriage to Mélisande and asks Pelléas to plead his case with Arkel: his grandfather was hoping for another marriage that would bring an end to long wars. Arkel listens to this story and decides not to intervene: since the death of his wife, Golaud has lived only for his son, and knows better than anyone what will make him happy. At this point, Pelléas joins them. He shares another letter with them: his friend Marcellus is about to die. Pelléas wishes to pay him one last visit. But Arkel objects: Pelléas cannot leave the bedside of his father, who is also ill, nor can he leave just as his brother returns. At Geneviève’s request, Pelléas leaves them to light a lantern to signal to the boat bringing Golaud home that he will be welcomed.

Mélisande, discovering the castle gardens, is disconcerted by their darkness. She meets Geneviève, who tells her about her arrival here forty years earlier and how one gets used to these places. They see Pelléas, who is also seeking the light. Together they stare at the sea and see the boat that brought Mélisande leaving in the distance. Geneviève leaves them to find Yniold and Pelléas walks Mélisande back to the castle.

Act 2
Pelléas leads Mélisande through the park to the fountain of the blind. Nobody comes here any more. It was a miraculous fountain, so they said, that restored sight to the blind. Mélisande is dazzled by the brilliance and beauty of the water. She plays with her ring, the one that Golaud offered her, throws it, catches it, but as midday rings out, the ring slips from her finger. It falls into the water, out of reach.

Mélisande is startled. Pelléas suggests telling Golaud the truth. In a room in the castle, Golaud, lying on his bed, tells Mélisande about the fall he had in the forest: just as noon was striking, his horse bolted for no reason. But his injuries are not serious. However, he is worried by Mélisande’s appearance. She admits that she is not happy in Allemonde. Golaud tries to understand, is it related to his mother, to Arkel, to Pélleas? These are places, replies Mélisande, from which you cannot see the sky. Golaud laughs at this childlike behaviour, when he suddenly notices that she no longer has the ring. He loses his temper, Mélisande says that she lost it in a cave, near the sea, while she was gathering shells for Yniold.

A furious Golaud orders her to go and look for it. With Pelléas. No matter that it is night-time. Pelléas and Mélisande are near the cave, at the water’s edge, waiting for the cloudy sky to clear so that they can enter in the moonlight. Mélisande must be able to describe the cave to Golaud. But as the light appears, she sees three old men sleeping inside and backs away. Pelléas, surprised, guesses that they have taken refuge there, exhausted by the famine ravaging the country. They leave the cave without entering it.

Pelléas must leave. He arranges a final meeting with Mélisande near the fountain in the castle grounds to bid her farewell for ever. Arkel is trying to raise Mélisande’s spirits when Golaud arrives. Irritated, he ill-treats his frightened wife until the king makes him see reason. Yniold is looking for his golden ball. In the distance he can see a flock of sheep being taken for slaughter. In their final leave-taking, Pelléas and Mélisande avow their love for each other. Golaud suddenly appears and kills Pelléas.

Mélisande flees, pursued by her husband. Golaud, who has grievously wounded Mélisande, watches over her bed with Arkel and a doctor. When the young woman regains consciousness, he desperately seeks to discover whether she has betrayed him with Pelléas. Mélisande dies, however, without having revealed her secret.