Children of Dune by Frank Herbert
As the book opens, Paul is believed to be dead, a martyr last seen nine years earlier. The political and religious empire he had created is prospering under his sister, Alia, who is acting as regent until Paul's twin children come of age. With indications of decadence already appearing, a mysterious Preacher is speaking out against the failings of this empire, and there are those who believe that this Preacher may be Paul.
One of the reasons that this book is stronger than the second book is the return of Lady Jessica, absent since the end of the first book. With her daughter Alia seeming possessed by the spirit of Baron Harkonnen (one of the great villains of sci-fi), Jessica becomes entangled in plots that could be fatal to her and her grandchildren. The twins themselves, intellectually far older than their physical ages and gifted with inherited talents, are hardly helpless in all this intriguing.
As Children of Dune begins, it is nine years since the Emperor Paul Muad'dib walked into the desert, blind. The ecological transformation of Dune continues apace and some of the Fremen are even living without stillsuits in the less arid climate. Fremen have started to move out of the Sietches and into the villages and cities. Millions of Fremen, thanks to the Jihad, have experience of life off planet or out of the desert, opening their minds to new possibilities yet also causing them to forget the old ways. It is a time of great social change and economic growth on the new capital planet of the Imperium, as more and more pilgrims arrive each day to experience the planet of Muad'dib and Alia.
The members of the Imperial high council — Alia, Duncan Idaho, Princess Irulan (who, since the death of Paul, has taken the role of caregiver to the Atreides children) and Stilgar — meet and lament the fact that they have lost the initiative in the political arena. Paul Atreides had been powerless to control the Jihad and had left only the shadow of his religious mantle. Now Alia and her council are even less capable of controlling it. They are finding themselves tightening their grip on politics and ritual, yet losing more control. The two young children of Paul, Leto II and Ghanima, are not normal nine year old children. Like Alia, they were forced into consciousness before birth and thus possess Other Memory, access to the lives and memories of all their ancestors. The children are very troubled because they have come to the conclusion that Alia has succumbed to what the Bene Gesserit call "abomination" — possession by one of her ancestors — and fear that a similar fate awaits them. They (and Alia) also realize that the quickening terraforming of Dune will kill all the sandtrout and thus bring to an end the Giant Worms, and inevitably to the spice itself.
Leto has an additional fear as well: he has started to have dreams which he is coming to believe are prophetic, like his father had when he was a similar age. He fears being locked into an early prescient vision as he suspects happened to his father before him. He also has the added pressure that Alia is pushing him to enter into an overdose-induced spice trance in order to unlock the door to prophetic visions. She feels the need for such visions in order to rule the empire, yet struggles to achieve them at all for herself.
Things have reached a heightened note of tension because Lady Jessica is coming to Arrakis to visit her grandchildren from her self-imposed retreat on Caladan. Alia fears this because she has indeed become possessed by the persona of her grandfather, the evil Baron Vladimir Harkonnen, and is sure that her mother will notice despite Alia's erroneous belief that no one has yet recognised the change in her. The Baron is leading her far away from the Atreides way of doing things: she has taken a lover behind Duncan's back, a priest called Javid.
Out in the desert, a new religious figure has arisen among the Fremen, who preaches against the injustices of the religious government and the changes among the Fremen. He is called 'The Preacher', and some even believe he is actually Paul Atreides.
Meanwhile, on Salusa Secundus, fallen House Corrino is plotting again for power. Princess Wensicia, younger sister of Irulan, rules in the name of her son Farad'n. She has plans for her son to become Emperor and has hatched a plot to assassinate the twins.