Complex sentence: Duncan and Jessica flee to Salusa Secundus, where Jessica begins to mentor the Corrino heir Farad'n, who seizes power from his regent mother and allies with the Bene Gesserit, who promise to marry him to Ghanima and support his bid for coronation as Emperor.
Split into simpler sentences: Duncan and Jessica flee to Salusa Secundus where Jessica begins to mentor the Corrino heir Farad'n. He seizes power from his regent mother and allys with the Bene Gesserit, who promise to marry him to Ghanima and support his bid for coronation as Emperor.