An unidentified speaker asks a knight what afflicts him. The knight is pale, haggard, and obviously dying. "And on thy cheeks a fading rose / Fast withereth too — ." The knight answers that he met a beautiful lady, "a faery's child" who had looked at him as if she loved him. When he set her on his horse, she led him to her cave. There she had sung him to sleep. In his sleep he had nightmarish dreams. Pale kings, princes, and warriors told him that he had been enslaved by a beautiful but cruel lady. When he awoke, the lady was gone and he was lying on a cold hillside.
"La Belle Dame sans Merci" is a ballad, a medieval genre revived by the romantic poets. Keats uses the so-called ballad stanza, a quatrain in alternating iambic tetrameter and trimeter lines. The shortening of the fourth line in each stanza of Keats' poem makes the stanza seem a self-contained unit, gives the ballad a deliberate and slow movement, and is pleasing to the ear. Keats uses a number of the stylistic characteristics of the ballad, such as simplicity of language, repetition, and absence of details; like some of the old ballads, it deals with the supernatural. Keats' economical manner of telling a story in "La Belle Dame sans Merci" is the direct opposite of his lavish manner in The Eve of St. Agnes. Part of the fascination exerted by the poem comes from Keats' use of understatement.
Keats sets his simple story of love and death in a bleak wintry landscape that is appropriate to it: "The sedge has wither'd from the lake / And no birds sing!" The repetition of these two lines, with minor variations, as the concluding lines of the poem emphasizes the fate of the unfortunate knight and neatly encloses the poem in a frame by bringing it back to its beginning.
In keeping with the ballad tradition, Keats does not identify his questioner, or the knight, or the destructively beautiful lady. What Keats does not include in his poem contributes as much to it in arousing the reader's imagination as what he puts into it. La belle dame sans merci, the beautiful lady without pity, is a femme fatale, a Circelike figure who attracts lovers only to destroy them by her supernatural powers. She destroys because it is her nature to destroy. Keats could have found patterns for his "faery's child" in folk mythology, classical literature, Renaissance poetry, or the medieval ballad. With a few skillful touches, he creates a woman who is at once beautiful, erotically attractive, fascinating, and deadly.
Some readers see the poem as Keats' personal rebellion against the pains of love. In his letters and in some of his poems, he reveals that he did experience the pains, as well as the pleasures, of love and that he resented the pains, particularly the loss of freedom that came with falling in love. However, the ballad is a very objective form, and it may be best to read "La Belle Dame sans Merci" as pure story and no more. How Keats felt about his love for Fanny Brawne we can discover in the several poems he addressed to her, as well as in his letters.