Once again a Dune prelude book chock full of information leading up to the novel originally written by Frank Herbert. This book takes place approximately 20 years after the Book "House Atreides" and about 30 years prior to the original. I will attempt to summarize the many plotlines with out giving away too much but I do warn you that some spoilers will exist.
Shaddam Corrino IV is the emperor and his Bene Gesserit wife, Anirul produces only daughters, leaving him without an heir to the throne. The emperor is aware of the Bene Gesserit ability to determine the sex of their children and grows annoyed at Anirul for not giving him a son. Along with this stress factor for the Emperor the Tleilaxu have yet to produce a synthetic equal to the Spice Melange. This was the reason the planet of Ix was taken over and House Vernius went renegade.
Dominic Vernius is still in hiding as a renegade but his children, Kailea and Rhombur, are living with Duke Leto Atreides on Caladan. Leto arranges fro Rhombur to take in a concubine from the Bene Gesserit, and Kailea becomes Leto's concubine. Kailea gives birth to Victor the son of Leto and heir to House Atreides, but due to politics and the fact that Kailea is considered renegade Leto cannot marry her. Besides, the Bene Gesserit have other plans with Jessica, the daughter of Vladimer Harkonnen and a Bene Gesserit witch. Leto does arrange to have a lady-in-waiting to help Kailea. Kailea's lady-in-waiting, Chiara, is actually a Harkonnen agent sent to poison Kailea's mind against Leto. Kailea and Chiara scheme to assassinate Leto thus making Victor the Duke and Kailea a Regent. But the plan backfires and the planned explosion kills young Victor and mutilates Rhombur. Kailea then kills Chiara and commits suicide unable to face what she has done.
The Tleilaxu offer to make a ghola,a clone, of Victor in exchange for the barely alive body of Rhombur Vernius. Leto ultimately refuses, after much soul-searching, knowing that the Tleilaxu intend only harm towards House Vernius. Instead, Leto hires Dr. Wellington Yueh, an expert in the field of cybernetics, to fashion a cybernetic replacement body for Rhombur. Leto and Jessica fall deeply in love, leading Jessica to decide to conceive a son for Leto's sake, directly disobeying the Bene Gesserit's order that she have a daughter.
Baron Harkonnen grows weaker due to his disease, but he becomes more vicious, destroying his half-brothers life (figuratively first then literally). A Suk doctor determines the cause of the illness is from the Bene Gesserit he raped. Harkonnen seeks reveng on the witches but through mind tricks they show him who is really in charge. Meanwhile, the Baron's brother, Abulurd, uncovers an illegal stockpile of spice on Lankiveil. Rather than turn his brother in to the Emperor, Abulurd, a benevolent ruler and the polar opposite of his brother Vladimir, uses the stockpile to benefit his people. Upon discovery of this, Glossu Rabban, Abulurd's firstborn son, strangles his father to death, an act which earns him the nickname of "Beast." Baron Harkonnen also kidnaps Abulurd's other son, Feyd-Rautha, and tries to raise him as his own.
We are also introduced to Gurney Halleck. Gurney's village is raided and his sister is taken away. He later finds she is forced to work in a "pleasure house" for the Harkonnen military. He tries to rescue her but is capture and made a slave. He then tries to attack Rabban, but is outnumbered and Rabban punishes him by killing his entire family. Gurney escapes to Salusa Secundus to help Dominic Vernius with his attacks against the empire.
Dominic learns of the atrocities going on on Ix and gathers all his stockpiles of atomics to the south polar region of Arrakis in order to deliver them to the homeworld of the Emperor and destroy the House Corrino. But his plan is discovered and the Sardukar guards are sent to stop him. Instead he detonates the atomics destroying most of the south pole area of Arrakis.
Gurney Halleck learns of this and goes to Caladan to pledge himself to Duke Leto Atreides.
On Arrakis it is learned that the Bene Gesserit have been mixing with the Fremen in order to blend prophecies of the Qwissatz Hadderach and the myths of the Missionaria Protectiva.
And this is only scratching the surface of this wonderful adventure into the Duniverse. Now for House Corrino, the final book of the prelude to Dune series, and one book closer to Dune.