Kevin J. Anderson & Brian Herbert 
Dune: House Atreides #3 [PDF ebook] 

Young Duncan Idaho is given an ultimatum: escape or die. Meanwhile, Leto Atreides is introduced to the hyper-advanced city of Ix where his future will be shaped in unimaginable ways. The Planetologist Pardot Kynes ventures into the plains of Dune, and makes a destiny-altering discovery. And Reverend Mother Gaius Mohiam confronts Baron Harkonnen with a proposition he can’t refuse…