The finale to the Prelude to Dune trilogy! 

Fearful of losing his precarious hold on the Golden Lion Throne, Shaddam IV, Emperor of a Million Worlds, has devised a radical scheme to create a synthetic alternative to melange, the addictive spice that binds the Imperium together, a substance that can be found only on the desert world of Dune. 

In subterranean labs on the machine planet Ix, Tleilaxu overlords use slaves and prisoners as part of a horrific plan to manufacture substitute spice. If this substance can supplant genuine melange, it will give Shaddam what he seeks: absolute power.