What bargain do the knight and the old woman strike?

In "The Canterbury Tales," the knight and the old woman strike a bargain wherein the knight agrees to marry her in exchange for her revealing the answer to his quest: what women truly desire. The knight is initially reluctant due to her old age and appearance, but he ultimately honors his promise. This bargain emphasizes themes of power, choice, and the nature of true beauty, as the old woman later transforms into a young and beautiful wife when the knight allows her to choose her form.