What is the main conflict in Heretics of Dune by Frank Herbert?

Heretics of Dune tells of life 3,500 years after the death of the Tyrant, Leto II, as ferocious "Honored Matres" stream in from the "Scattering," and the Bene Gesserit work to unite a ghola, Duncan Idaho, and a Fremen girl, Sheeana, who has the power to command worms. The Tleilaxu, who have been hiding for millennia behind self-built walls, are ready to claim their place in the universe, aided by a document prepared by the Sisterhood. Ancient Dune - Rakis - is destroyed and a lone worm is rescued to begin a new cycle on Chapter House Planet.