Buttercup is the princess of the fictional country, Florin. She has a farmboy named Westley. Whenever Buttercup asks Westley to do something, he always replies, "As you wish". Buttercup eventually realizes that when he says as you wish, that is his way of telling her that he loves her. Buttercup soon realizes that she feels the same way for Westley, and the two plan to get married. Westley goes out to seek his fortune, but unfortuanely, is attacked by pirates lead by the Dread Pirate Roberts, and they presumably kill him, as they have a reputation of never sparing anybodys life. This leaves Buttercup heart broken.
Five years later, Buttercup reluctantly agrees to marry Prince Humperdinck, as she still believes Westley to be dead. However, before the wedding, Buttercup is kidnapped by a man named Vizzini, and his two assistants, Fezzik (a giant), and Inigo Montoya. They are also followed by Humperdink, and a myserious Man in Black. The Man in Black saves Buttercup, but Buttercup believe him to be the Dread Pirate Roberts. Buttercup psuhes him into a gorge, and tells him he should die. However, the Man in Black replies to this by saying, "as you wish", as Buttercup realizes that this man is Westley. Buttercup is ecsatic to discover that Westley is still alive, and dives into the gorge after him. The two are happy to be reunited, and plan to run away together. Westley explains that he was held prisoner by Roberts until Roberts revealed he was not the original Dread Pirate Roberts and the original was long retired and the title was passed on throughout the years. The "Roberts" Westley knew then retired and gave Westley the title. Westley then decides to retire from piracy since he now has Buttercup. Unfortunately, the two are found by Humperdink and his vizer Count Rugen. He then forced Buttercup to marry him, and ordered Westley's execution. Buttercup only agrees to go with him, if they spare Westley's life. Humperdink agrees, but secretly has Rugen imprission and torture Westley.
When Buttercup expresses unhappiness at marrying Humperdinck, he promises to search for Westley, but his real plan is to start a war with the neighboring country of Guilder by killing Buttercup and framing them for her death. In fact, he was the one who ordered Vizzini to kidnap Buttercup. When Buttercup realizes this, she taunts Humperdink, until he becomes so enraged that he tortures Westley to death. Humperdink then orders his and Buttercup's wedding.
Meanwhile, Fezzik and Inigo Montoya come to the rescue, by bringing a man named "Miracle Max" who is able to bring Westley back to life, as he says, Westley is "only mostly dead". Westley, Fezzik, and Inigo Montoya then invade Humperdink's castle. This prompts Humperdink to order a drastically-abridged version of the wedding ceremony, and then rushed Buttercup to her chambers.
Westley finds Buttercup, and she is about to commit suicide, not able to accept the fact that she and Humperdink and now married. However, Westley assures her that they are not married, because she never said "I do". Westley then scares Humperdink, and Buttercup ties him to a chair, leaving him to contemplate his cowardice.
Westley and Buttercup then ride off together, and share a passionate kiss.