Buttercup is a farm girl who lives in the country of Florin and is the true love of Westley. When he works on her family's farm, Buttercup refers to him only as "farm boy" and loves to order him around. Westley would not argue with her but would only obey her commands and reply "As you wish." Over time, she realizes that when Westley says "As you wish" he is really saying "I love you." In time, she realizes that she loves him just as strongly, too.
When Westley goes away to find his fortune, his ship is attacked by the Dread Pirate Roberts, and the story gets back to Buttercup that her love has been killed by the pirate who never takes prisoners. Devastated to learn this, Buttercup shuts herself away in her room, forgoing sleep and food. In the end, she decides that, while she may live on, she will never love again.
Five years later, Buttercup is forced to become betrothed to Prince Humperdinck. Although she does not love him and tells the prince so, Humperdinck pushes forward with the wedding, assuring her that, with time, she will come to love him.
While she does not like the idea of marrying her prince, she does still enjoy riding her horse. While out one day, she comes across three men claiming to be lost circus performers and, before she can do anything, is knocked unconscious. When she awakes, she realizes she's now on a boat in the middle of the sea, kidnapped by the men, who she learns are names Vizzini, Inigo, and Fezzik. Vizzini, the band's leader, announces his plans to start a war with the neighboring country of Guilder by killing the princess and leaving her body on Guilder soil. The other two men don't seem keen on following this plan and an argument breaks out. Later, they are sailing through the night when they see a ship in the distance following them. Buttercup uses this opportunity to jump out of the boat and into the water with creatures known as the shrieking eels(which look like leviathans rather than modern day eels).
Before she could be eaten, she gets pulled back on board by the men, and is taken to a cliff to escape from the boat chasing them. The three men carry her up with Fezzik climbing a rope. The person driving the boat (a man in a black attire and a mask) rushes up to follow. Vizzini cuts the rope, but the stranger clings to the side of the cliff.
He tells Inigo to kill the man while they escape. The stranger defeats the swordsman and continues to follow them. Unhappy with this, Vizzini tells Fezzik to kill him. The giant fails to do so as well, so Vizzini takes Buttercup to the top of the cliff. He blindfolds her at a rock slab, sets out some wine, points a daggar at her throat, and patiently waits for the man in black to make his appearance. He does do so, and tells Vizzini that they will have a battle of the wits, with the winner getting the princess, and the loser facing death. He then takes some iocane powder, turns his back, and after a bit faces Vizzini once more. He states that one of the drinks is poisoned with the powder, and that Vizzini gets to choose the cup he will drink from.
Clearly thinking he is too smart, Vizzini distracts the man in black, switches the glasses, and they take a drink. The stranger calmly tells the cackling Vizzini he is wrong. Vizzini laughs a bit more, before dying. Buttercup questions the man about why he poisoned his own drink, and the man tells her he has immunity to iocane powder, therefore bother glasses are poisoned. He leads her away.
After a while, they stop to rest, and Buttercup asks who he is. The man won't say, so she concludes that he is the Dread Pirate Roberts. The man admits this with pride, before teasing and tormenting her about him killing Westley. The prince, who has come to rescue Buttercup, appears over the distance with many men. Angry, she pushes Dread Pirate Roberts down a hill, yelling at him to die. On his way down, he yells out the words Buttercup has been aching for for 5 years. "AAASSS YOOUU WWWIIISSHHHH!" Realizing her lover is alive and that she just pushed him off a hill, she throws herself down, too. At the bottom of the hill, they share a heartfelt kiss.
They run into an infamous swamp where noone has left alive, and after some drama involving a giant rat, they emerge from the swamp. The prince threatens to kill Westley, but Buttercup tells him to return her lover to his ship, and in return she will go with him. After she left, Westley notices that the Count had six fingers on his right hand. Before their dual, Inigo told him that a six fingered man killed his father, so as soon as Westley points this out, he is knocked unconscious.
Buttercup has a horrible dream involving her betraying Westley. She wakes up and tells the prince that she won't marry him. Being His Royal Douchebagginess, the prince refuses to let her go(he wants to kill her to start a war. Don't ask.) And Buttercup is force to marry him.
After the wedding, Buttercup goes to her chamber, dagger aimed at her heart, planning to die. Before she can do so, Westley remarks from behind that she should not damage her perfect body. She turns to find him lying on the bed, too weak to move(Long story. Summary: He became mostly dead, Inigo and Fezzik brought him back since they liked him, and now he's only a bit dead, unlike before). Buttercup, overcome by joy, throws herself at her lover, kissing him.
Their happy reunion is sadly cut short when the prince comes in, sword in hand, and threatening to kill them. To stall, Westley rambles on about how everyone is going to hate the prince when he gets his body cut up. Then, with just enough energy, he stands up and points his sword at the prince, pretending he has his strength back. Knowing he's no match for Westley, the evil ruler drops his weapon and backs off into a chair. Buttercup ties him up.
Inigo comes in, bleeding from his dual with the Count, and asks Westley where Fezzik is. Westley states that their comrade is not with him. He starts to walk forwards, but falls due to his incapability to support himself. Buttercup overcome with worry, goes to help.
Anyways, after some chaos, Westley, Buttercup, Inigo and Fezzik all ride out from the castle on white horses, leaving Humperdinck to wallow in his guilt and self pity for the rest of his life.
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