He became a saint without a god, every word a blasphemy.” But by the fourth book, “God Emperor of Dune,” Leto II has ... when Herbert brings back Duncan Idaho, the ludicrously named sword ...
However, what remains constant in the series are the Bene Gesserit order, and Duncan Idaho ... Heretics of Dune takes place 1500 years after God Emperor of Dune's heavily built-up events.