The sea-world of Pandora, so unlike waterless Dune, is similar in one fateful way - its struggle for survival. An awesome conflict, one that will either transform or destroy the planet, has divided the people of Pandora: the dictator, the sadistic Raja Flattery ... its resistance and anachristic Shadows (who may or may not exist) ... and its promised savior, the beautiful near-human Crista Galli, who was raised undersea.
Now the remnants of humanity, having mastered the Void and transformed new worlds, depart once more for the waiting stars.
But this time, Man does not go alone.
This is listed in the book as Frank Herbert's final work.