Baron Harkonnen’s plans are coming to fruition: Thufir Hawat, the master of assassins, intercepts a note, allegedly from the baron to Lady Jessica, that implicates her in a plot to betray Duke Leto. The duke does not believe the allegation, but he recognizes it as a Harkonnen plot, and he decides that in order to trap the Harkonnens, he must pretend to fall into the trap. He decides to allow Hawat and Duncan Idaho, his swordmaster, to think that Jessica may be guilty, though he does not actually believe the allegations.

Some of the Fremen have started calling Paul the Mahdi, or “the one who will lead us to paradise.” This follows the prophecy that their messianic savior will arrive as the child of a Bene Gesserit, like Jessica.

The duke tells Paul about the Harkonnen plot to turn the duke against Lady Jessica but warns him to tell no one else. The duke has plans to use his “propaganda corps” to secure the loyalty of the people of Arrakis, but he warns Paul that if anything goes wrong Paul should make use of his Mahdi status to gain the Fremen’s respect.

The duke and Paul then meet Dr. Kynes, the Arrakis ecologist. Kynes has been ordered to betray the Atreides, but he finds himself impressed by them despite his low expectations of their character. Kynes explains the use of stillsuits, special outfits that contain the amount of moisture the body uses up and which are able to recycle the majority of the body’s moisture. As Kynes interacts more and more with Paul, he finds that Paul oddly seems to fit the legends of the Mahdi. Kynes is also surprised to find that Leto is a penetrating man who seems interested in Kynes’s plans to make Arrakis an Edenic paradise.

Kynes takes the duke and Paul to visit a spice-mining operation. While they are there, the roaming spice factory is attacked by a giant sandworm. The duke takes control and makes sure to save all the miners, leaving the spice behind. The duke’s concern for human life over spice impresses Kynes. As the duke leaves and his ship flies away, Paul spots two men that he correctly identifies as Fremen, though Kynes tries to hide that fact. Paul’s mysterious skills and the duke’s concern for his workers’ lives impress Kynes even more.

The duke holds a dinner party for the distinguished members of Arrakeen society, the wealthy members of the planet. Kynes attends, and he is surprised when Jessica expresses her hope that one day Arrakis will be a lush paradise. Kynes asks her if she brings “the shortening of the way,” which translates to Kwisatz Haderach. Jessica does not have the chance to answer, but it is clear that Kynes is becoming more intrigued by Jessica and Paul.

At the dinner party, Jessica realizes that there is at least one spy present, a Guild banker. Paul seems to have recognized the banker’s behavior as well and banters with him. Jessica notes that the banker seems to be terrified of Kynes. The duke engages Kynes in discussing the possibility of changing Arrakis’s climate, and Kynes reluctantly admits that there may be enough water on Arrakis to start the process of making it an Eden.

The third section introduces a complex set of character interactions. The plot becomes increasingly dense and almost incomprehensible. At the center of the plot is a new character, Dr. Kynes. We already know that Dr. Kynes, the ecologist, or, as he calls himself, planetologist, has been ordered to sabotage the Atreides’s efforts at making any money off Arrakis. However, Kynes’s initial agreement to sabotage the Atreides was more due to his own desire to hurt the Atreides’s plan, rather than due to the Harkonnens’ bribing or bullying. Thus, Kynes is surprised when the Atreides quickly earn his respect. Kynes is impressed by Duke Leto’s honest concern for the lives of men that he has not even met, and Paul fascinates him because he fulfills many of the Fremen prophecies. Paul’s role as a Mahdi for the Fremen is important to Kynes since Kynes is Liet, a godlike figure for the Fremen. Kynes’s fascination with Paul becomes more important later in the novel. For now, Kynes is still watching and weighing his options.

The dinner scene in this section is one of the funniest and most macabre scenes in the book. The dinner party is an uncomfortable affair, with many people using one another to further their own goals. Duke Leto uses the dinner as an opportunity to analyze the elite members of the new Arrakis world, but he also embarrasses himself by making it clear how much he intends to change their lifestyle by changing the planet’s ecology. Leto is also tortured because he must pretend that he distrusts his wife. Kynes has an alliance with Tuek, a head smuggler on Arrakis, and can intimidate the Guild banker-spy. Jessica recognizes that the banker is a Harkonnen spy, and there is a tense scene in which Paul nearly gets in a fight with him. Paul and Jessica are also aware that Kynes tells several lies in the course of the dinner. As for the rest of the dinner party attendees, they are interested in finding out how they can take advantage of their new rulers. Herbert fills the party scene with tension and humor while revealing a wealth of information about the characters.

The placement of the dinner-party scene within the scope of the novel is important. The dinner party represents the high point of the duke’s brief reign on Arrakis. From here on, problems will mount as the Harkonnen trap unfolds and unravels the duke’s power. Throughout the dinner celebration, there is a sense that the duke’s reign is fated to end, which the reverend mother emphasized earlier in the novel. Thus far, Herbert imbues the tone of Dune with a sense of fatalism—and the feeling that once certain events are put into motion, they will progress to a particular unavoidable conclusion. For instance, Jessica and the reverend mother knew that once the emperor gave Arrakis to the duke, the duke’s situation was hopeless—he would fail and most likely die. Paul is already beginning to develop a premonition of doom, and he struggles with this “sense of terrible purpose” throughout the novel.