Dune opens on the planet Caladan with House Atreides, who have been told by the Emperor of the Known Universe to take charge of the planet Arrakis. Arrakis, AKA Dune, is an almost inhospitable desert planet with a hostile, mysterious native population known as the Fremen. Arrakis is pivotally important because it’s the only known source of melange, or spice, an addictive substance that lengthens youth and allows some people to gain “prescience” or awareness of the future. Without spice, space travel would be impossible, because a safe path through the known universe can’t be charted without a navigator using spice.
House Atreides is run by Duke Leto, who has a 15-year-old son, Paul Atreides, with his concubine, Lady Jessica. Jessica is a sister of the Bene Gesserit, meaning she’s trained in a lot of special skills, including controlling her body and mind, sensing if others are telling the truth, and using the Voice, which can force people to follow commands (within limits). She’s been training Paul in the Bene Gesserit way, believing he could be the Kwisatz Haderach. The Bene Gesserit have been trying for 90 generations to breed the Kwisatz Haderach, a man who can survive seeing into the future the way a Bene Gesserit does. Paul has prophetic dreams, so it’s possible he’s the one they’re looking for. Jessica’s teacher tests Paul with a gom jabbar (a poisoned needle) and a box that causes enormous pain. Though he withstands more pain than any person before him, the test isn’t conclusive as to whether he’s the Kwisatz Haderach.
Duke Leto and the rest of the Atreides know they’re walking into a trap on Arrakis. The Atreides’ mortal enemies, House Harkonnen, used to control Arrakis, and they’ve certainly got plans to destroy House Atreides. The Harkonnens are sadistic, cunning, and gluttonous; their leader, Baron Vladimir Harkonnen, is especially terrible and hates Duke Leto. They’re supported by the Emperor himself, who wants to get rid of Duke Leto primarily because of his popularity and military strength. The Harkonnens have a secret agent in House Atreides, Dr. Wellington Yueh, who helps the Harkonnens invade Arrakis, capture the Duke, and kill almost all of House Atreides; however, Dr. Yueh gives the Duke a poisoned pill he tries to use to kill the Baron Harkonnen, and Dr. Yueh helps Paul and Jessica escape into the desert of Arrakis.
In the desert, Paul’s extensive training combines with a large intake of spice, and his awareness blossoms into an advanced prescience. The Fremen have legends of the Lisan al-Gaib, an Outer World prophet (these legends were actually created by the Bene Gesserit—hundreds of years ago, a Bene Gesserit came to Arrakis and implanted these stories as a sort of safety route for other sisters, so they could arrive on a planet and be “the One”). Paul and Jessica are found by Fremen, thanks to the help of the Imperial Planetologist and secret leader of the Fremen, Liet-Kynes, who dies shortly after.
The Fremen believe that Paul and Jessica are the ones foretold by legend, so they’re protected by Stilgar, the fierce but reasonable leader of Sietch Tabr. To be accepted among the Fremen, Paul has to kill one of them in one-on-one combat. Shortly after, Paul takes the Fremen name “Muad’Dib” (desert mouse), Jessica drinks the Water of Life and becomes the Reverend Mother of the sietch, and Paul forms a deep bond with Chani, Liet-Kynes’s daughter, the young woman Paul has seen in his dreams for years.
A few years pass, and the mythology around Paul–Muad’Dib grows. Jessica is concerned about the fanatical following he attracts. His advanced awareness allows him to see into the past and future, and he sees a number of concerning things, including a jihad across the universe—a bloody religious war under the Atreides banner. He plans to stop this from happening at all costs. He also learns that Jessica, unknown to her, is the daughter of Baron Harkonnen, making Baron Harkonnen Paul’s grandfather.
Paul wants revenge against the Harkonnens and Emperor, and he works with the Fremen to accomplish this. The Fremen want to make Arrakis hospitable to human life, and thanks to Liet-Kynes’s ecological framework, they’ve collected secret vast reserves of water and have begun changing the surface of Arrakis. Paul now has a son with Chani, Leto II, and Jessica has given birth to Paul’s sister, Alia, who is strangely intelligent—this is because she was in the womb when Jessica drank the Water of Life, so the process changed Alia as well.
The Harkonnens, meanwhile, are in a difficult spot. Baron Harkonnen wants to make a move against the Emperor to gain more power, but his chosen successor, his nephew Feyd-Rautha, is attempting to assassinate him and gain control. They’ve left his other nephew, Rabban, in charge of Arrakis for the last few years, knowing he’ll be so terrible to the people of Arrakis that they’ll welcome his replacement (Feyd-Rautha) as a hero.
Life on Arrakis is complicated by the presence of sandworms, or “makers” as the Fremen call them—enormous toothed worms that live in the desert and are intensely territorial. As he gets more powerful and more enmeshed in Fremen culture, Paul learns how to ride sandworms. He also chooses to drink the Water of Life, which will kill him if he isn’t the Kwisatz Haderach. He survives, and his power grows immensely. He has a vast understanding of the future possibilities, as well as the Now, which includes knowledge that the Emperor, House Harkonnen, the Guild, and others are all hovering around Arrakis, looking for Muad’Dib, ready to take control of Arrakis. Unfortunately, as Paul prepares for battle, the Emperor raids a Fremen sietch, killing Leto II and taking Alia hostage. When he tries to grab her, Alia kills Baron Harkonnen with a gom jabbar.
After a major battle between Fremen and the outworlders, Paul-Muad’Dib is victorious, and he meets with the Emperor, the Guild, and Feyd-Rautha Harkonnen. Feyd-Rautha challenges him to a duel, and even though Feyd cheats, Paul wins and kills him.
From his prescience and time with the Fremen, Paul has learned that sandworms don’t only eat spice, they make it. By combining certain elements of the sandworm life cycle, he can actually destroy every sandworm on Arrakis, therefore destroying all spice. He leverages his ability to destroy spice into complete control over the Spacing Guild. This means he controls all travel anywhere in the known universe. It also means he has power over the Emperor, whom he forces to essentially give up all power—all of his financial holdings, his military position, and even his daughter, Princess Irulan, whom Paul agrees to marry so he is next in line to the Imperial Throne. Paul promises Chani that he’ll never even look at Irulan fondly. Paul makes plans to reward the people who have helped him, especially the Fremen, and he asks Jessica and Chani to help negotiate the specifics of their changed universe.
