The Bene Gesserit Sisterhood fights for survival on their home planet Chapterhouse as the Honored Matres continue their violent conquest of the known universe, while a new Duncan Idaho ghola and a renegade Honored Matre become central figures in a desperate gambit. The Sisterhood races to breed sandworms and control spice production while uncovering the true nature of the enemy driving the Matres. Herbert's final novel ends on an unresolved, intentionally open-ended note.