Prince Golaud, grandson of King Arkel of Allemonde, has become lost while hunting in the forest. He discovers a frightened, weeping girl sitting by a spring in which a crown is visible. She reveals her name is Mélisande but nothing else about her origins and refuses to let Golaud retrieve her crown from the water. Golaud persuades her to come with him before the forest gets dark.
Six months have passed. Geneviève, the mother of the princes Golaud and Pelléas, reads a letter to the aged and nearly blind King Arkel. It was sent by Golaud to his brother Pelléas. In it Golaud reveals that he has married Mélisande, although he knows no more about her than on the day they first met. Golaud fears that Arkel will be angry with him and tells Pelléas to find how he reacts to the news. If the old man is favourable then Pelléas should light a lamp from the tower facing the sea on the third day; if Golaud does not see the lamp shining, he will sail on and never return home. Arkel had planned to marry the widowed Golaud to Princess Ursule in order to put an end to "long wars and ancient hatreds", but he bows to fate and accepts Golaud's marriage to Mélisande. Pelléas enters, weeping. He has received a letter from his friend Marcellus, who is on his deathbed, and wants to travel to say goodbye to him. Arkel thinks Pelléas should wait for the return of Golaud, and also reminds Pelléas of his own father, lying sick in bed in the castle. Geneviève tells Pelléas not to forget to light the lamp for Golaud.
Geneviève and Mélisande walk in the castle grounds. Mélisande remarks how dark the surrounding gardens and forest are. Pelléas arrives. They look out to sea and notice a large ship departing and a lighthouse shining, Mélisande foretells that it will sink. Night falls. Geneviève goes off to look after Yniold, Golaud's young son by his previous marriage. Pelléas attempts to take Melisande's hand to help her down the steep path but she refuses saying that she is holding flowers. He tells her he might have to go away tomorrow. Mélisande asks him why.
Pelléas et Mélisande. (2022, December 15). In Wikipedia. https://en.wikipedia.org/wiki/Pell%C3%A9as_et_M%C3%A9lisande_(opera)