The outline of the story is simple. Prince Golaud encounters the weeping Mélisande in a forest. He marries her, and takes her back to the castle of his aged grandfather, King Arkel. She and his much younger half-brother, Pelléas, become close. Golaud grows jealous and, catching the two together, kills Pelléas. Mélisande gives birth to a baby girl, and dies.
However, the play, and Debussy's setting of it, are anything but simple. Mélisande is a mystery—no one knows who she is, or where she came from. The actual relationship of Pelléas and Mélisande is not clear. The atmosphere of the castle itself, permeated with age and death and surrounded by dark forests where no one can see the sky, is as much of a character as any of the humans. There are continual references to blindness.