A knight in King Arthur's court rapes a young woman he sees walking from the stream one day. As punishment, the queen decides that he must go on a quest to learn what it is that women most desire.
Returning to Arthur's court at the end of an unsuccessful search, the knight meets a loathly lady who offers to tell him what women most desire if he promises to grant her next request. He agrees, and is able to answer the question successfully. The loathly lady's request, however, is that the knight marry her. He does so reluctantly, but refuses to sleep with his wife on their wedding night. Sensing her husband's discomfort, the loathly lady offers him a choice; he can have her ugly and old but faithful, or young and beautiful with no guarantee of fidelity.
The knight asks his wife to choose for him, in effect yielding sovereignty to her. Pleased with his answer, the loathly lady becomes a young beautiful maiden who's also faithful to her husband, and the two live happily ever after.