The God-Emperor is dead but the effects of his long reign continue. Much time has past and the human race struggles with new threats. This is the setting for the Heretics of Dune.
Part of what is happening is the return from the Scattering. People descended from those who had left the old empire are returning, including the dangerous Honored Matres, a version of the Reverend Mothers but with a twist.
The God -Emperor had commissioned new gholas of Duncan Idaho and that project continues. But the newest version has been changed in some mysterious way. Meanwhile, a young girl on Dune has the strange ability to control the worms.
This book is one of the better ones in the series. It does not drag near as bad as the previous book. There is much more action.
The Dune series is not for everyone but for those who like this style, it is some of the best science fiction.