Shaddam Corrino IV finally sits upon the Golden Lion Throne, enjoying his position as Padishah Emperor of the Known Universe. However, his rule as Emperor is precarious at best, as his wife, Anirul, has been instructed by her Bene Gesserit sisterhood to bear him only daughters. His authority is also challenged by the powerful House Harkonnen, whose illegal stock-piling of the spice melange is of great concern to the Emperor. In order to monopolize the spice, Shaddam and his trusted advisor and friend, Hasimir Fenring, plan to synthesize the substance with the help of Hidar Fen Ajidica, a Tleilaxu Master Researcher. Ajidica sets up laboratories to accomplish this purpose on the newly conquered planet of Ix, formerly the home of House Vernius. By the end of the novel, Ajidica tells Fenring that the manufacture of synthetic spice has been a success, although the validity of his claim is highly dubious.
Meanwhile, on Caladan, Duke Leto Atreides bids Duncan Idaho farewell. Duncan is headed for Ginaz, where he will study to become a swordmaster. Leto and his friends, Kailea and Rhombur Vernius, are still struggling to liberate the siblings' former homeworld, but they have made little progress so far. Kailea becomes Leto's concubine, though he refuses to marry her for obvious political reasons. Rhombur seeks out a companion from the Bene Gesserit order and is matched with a young woman named Tessia who gives him a new sense of drive and purpose. After receiving a plea for help from C'tair Pilru, an Ixian rebel, Rhombur begins supplying the Ixian resistance with limited aid, though his attempts are greatly hindered by the Emperor's Sardaukar. Kailea soon gives birth to Leto's son, Victor. After the child's birth, she becomes increasingly dissatisfied with her role as Leto's concubine, wanting the Duke to marry her so that their son can succeed his father someday. Kailea's lady-in-waiting, Chiara, is actually a Harkonnen agent sent to poison Kailea's mind against Leto.
