Following the downfall of House Atreides at the hands of House Harkonnen, Princess Irulan, the daughter of Padishah Emperor Shaddam IV, documents her father's treason against the Atreides lineage. As events unfold on the desert planet of Arrakis, Stilgar and his Fremen warriors escort Paul Atreides along with his expectant Bene Gesserit mother, Lady Jessica, to the mysterious Sietch Tabr. While some Fremen express their distrust and speculate the arrival of spies, Stilgar and others are intrigued by the notion that a mother and son from the "Outer World" might fulfill prophecies and bring prosperity to their barren land.
The Fremen eventually accept Paul, but Stilgar warns Jessica that she must take on the mantle of Sietch Tabr's dying Reverend Mother by drinking the perilous Water of Life—a substance often lethal to males and the untrained female. Harnessing her Bene Gesserit skills, she miraculously transforms the deadly liquid and survives, gaining access to the memories of all past Reverend Mothers. Additionally, the substance prematurely awakens the consciousness of her unborn daughter, Alia, allowing for a rare communion between mother and child. They both agree that convincing the skeptical northern Fremen about the prophecy should be their priority. Chani and her companion Shishakli suspect that the prophecy was a fabrication designed to control the Fremen, though Chani starts to hold Paul in high regard when he professes his intent to fight alongside the Fremen instead of seeking dominion over them.
As Paul and Chani's romance blossoms, Paul immerses himself in the Fremen way of life, learning their language, becoming a Fedaykin warrior, riding the largest sand-worm ever seen, and launching raids on Harkonnen spice operations. He adopts the identities of "Usul" and "Muad'Dib." In reaction to the ongoing spice raids, Baron Harkonnen replaces his brutish nephew Rabban with his cunning younger nephew, Feyd-Rautha, to tighten control over Arrakis. Lady Margot Fenring, another Bene Gesserit, is dispatched to evaluate Feyd-Rautha’s potential as a Kwisatz Haderach and to ensure his genetic legacy.
Jessica sets off to unite with fervent Fremen believers in the prophecy, while Paul remains in the northern territories, haunted by visions of a catastrophic holy war if he pursues a messianic path south. In a bold raid against a smuggler spice harvester, Paul reunites with Gurney Halleck, who helps him discover the hidden nuclear stockpiles of House Atreides. In retaliation, Feyd-Rautha orchestrates a brutal assault on the northern Fremen, annihilating Sietch Tabr, killing Shishakli in a horrific blaze, and forcing Paul and the remaining fighters to journey southward. Upon their arrival, Paul drinks the Water of Life and plunges into a comatose state. This infuriates Chani, but Jessica persuades her to blend her tears with the liquid, ultimately reviving Paul. Now equipped with a glimpse into the intricacies of space and time, he witnesses an adult Alia amidst the waters of Arrakis and identifies a singular path to victory—understanding that Jessica is, in fact, Baron Harkonnen's daughter.
At the southern Fremen war council, Paul kindles enthusiasm by revealing his ability to they deeply understand their thoughts. He declares himself the Lisan al Gaib, challenging Shaddam, who promptly arrives on Arrakis accompanied by Irulan and the formidable Sardaukar troops. Shaddam reprimands the Harkonnens for their blunders and terminates the Baron's life support. The Fremen mobilize an offensive, utilizing nuclear devices and sand-worms to motivate the Sardaukar into retreat. Paul confronts the Baron and captures Shaddam alongside his court. Gurney leads a pivotal charge against Arrakeen, ultimately vanquishing Rabban.
Paul challenges Shaddam for the throne and, to Chani's dismay, asserts the necessity of marrying Irulan. The Grand Houses, summoned by the Baron, appear ready to invade, yet Paul threatens to obliterate the spice fields with nuclear weaponry should they interfere. Feyd-Rautha steps up as Shaddam's champion, but Paul ultimately claims victory in the duel despite sustaining two stab wounds. Irulan consents to the marriage on the condition that her father is spared. Although Shaddam capitulates, the Great Houses reject Paul’s claim to the throne, prompting him to direct the Fremen to assault the hovering fleet. As Stilgar leads the charge onto captured Sardaukar ships, Jessica and Alia reflect on the impending commencement of Paul's holy war. Chani, unwilling to submit to Paul, forsakes him and rides off alone on a sand-worm.
