The Princess Bride begins with William Goldman's discussion of his life, his family, the book itself (written, he assures us, by S. Morgenstern), and its relation to his own childhood and adulthood. He proclaims that it is his favorite book and that he has edited out the "good parts," the action stories that his father read to him when he was ten and in bed with pneumonia.
The story proper begins with Buttercup, one of the world's twenty most beautiful women, and her tomboyish life on a farm with her parents, her horse, and Westley, their farm-boy. One afternoon a band of Florinese royalty appear on the farm, and while Buttercup watches a well-dressed Countess watch Westley, she falls suddenly, madly, jealously in love with this man she has known all her life. She professes her love to him, and he leaves immediately to America to seek his fortune, and soon is reported to have been murdered by the Dread Pirate Roberts. Buttercup is broken, and vows never to love again.
The next three chapters are short and deal primarily with the wedding preparations of Prince Humperdinck. We learn that he loves to hunt, is quite good at it, and spends the majority of time in his Zoo of Death (the original "Pit of Despair") hunting the vile and dangerous animals he has collected there. His father, King Lotharon, is old and dying, and Prince Humperdinck must marry to take his place as Florin's king. After an unfortunate occurrence with the princess of Guilder, he is led to Buttercup by his confidante, Count Rugen, and he demands her hand in marriage.
In Chapter Five, Buttercup is kidnapped by a criminal band consisting of Vizzini, Fezzik, and Inigo. Followed closely by a mysterious black boat, they sail with her to the cliffs on the coast of Guilder. On the coast, each of the men is defeated in his strength by their pursuer, the man in black, and while Inigo and Fezzik, after a sword-fight and wrestling match, respectively, are left unconscious but alive, Vizzini is killed in a battle of wits. The man in black runs with Buttercup along the Guilder terrain, and soon is revealed to be the long-lost Westley. The lovers reunite and, in an attempt to avoid capture by Prince Humperdinck and his men, Buttercup and Westley travel through the Fireswamp, an eerie and dangerous place. We find out here that Westley is the pirate that everybody had assumed had killed Westley. Upon exiting the swamp, they encounter Humperdinck anyway, and Buttercup agrees to return with the prince to Florin as long as he promises to return Westley safely to his ship. The lovers are separated again.
Chapter Six follows each of the main characters in their plans leading up to the wedding between Buttercup and Humperdinck. Inigo and Fezzik reunite in the Florin Thieves Quarters and set out to find the man in black. The man in black (Westley) is currently being tortured in the Zoo of Death by Humperdinck and Count Rugen. Buttercup is having nightmares and pining away for Westley, who in turn is still pining away for her. Humperdinck is planning to murder Buttercup on their wedding night in order to frame Guilder and begin a war. Everybody is harried and busy as the wedding approaches. Humperdinck reassures Buttercup that he has sent out his four fastest ships to find Westley, Buttercup realizes that he is lying and calls him a weakling, and Humperdinck us terribly offended by this and rages off to the Zoo of Death to kill Westley on the torture machine. Inigo and Fezzik hear Westley's scream and follow it to the Zoo of Death.
Chapter Seven plots Inigo and Fezzik inside the false entrance to the Zoo of Death, where they must pass many ghastly creatures before descending to the fifth level and finding Westley. The highlights of this underground journey are a ravenous snake and King bats, and Fezzik and Inigo respectively save each other's life. On the bottom level, they finally find Westley's corpse, and they drag him to Miracle Max's house in hope of reviving him. Miracle Max and his wife Valerie are feisty and difficult and reluctant to help, but they are very experienced in miracles, so once they set out to revive Westley, they create a successful miracle pill which does the trick. Inigo and Fezzik administer it to Westley on the top of the castle wall, and Westley comes back to life instantly and concocts a plan for them to enter the castle proper. This plan involves Fezzik being lit on fire and wheeled toward the guards, and it works without a hitch.
Chapter Eight follows the final acts of the main characters, first tracing Inigo as he challenges, chases, is wounded by and ultimately kills Count Rugen. Buttercup is married to Humperdinck, left in his chamber where she plans to kill herself when she sees Westley, alive on the prince's bed. Westley frightens Humperdinck with talk about how he would leave him alive but maimed if they were to duel, and the prince allows himself to be tied to a chair by Buttercup. Meanwhile, Fezzik, who has gotten lost on the grounds, appears with the prince's four white horses, and he, Inigo, Westley and Buttercup ride away. S. Morganstern ends the book with a series of ominous crises, but William Goldman cuts in and says that he believes that they do escape and live happily, though not perfectly, ever after.