Will somebody please tell Mr Simmons that chase stories are supposed to be fun! This book is essentially a chase on a galactic scale and Mr. Simmons manages the not inconsiderable feat of making an inter-galactic chase extremely, painfully, unbelievably dull and boring!
Its 270+ years since the Time Tombs opened. The WorldWeb is no more, the farcasters do not work anymore and the fatline has gone silent. Most of the worlds of the erstwhile Hegemony are now governed by a new government, the Pax, which is controlled by the resurgent Church. Lenar Hoyt has become the Pope and the cruciform parasites have been tamed and are now offered by the church to every born-again christian offering immortality. It is in this world, dominated by this Church, that the 12-year-old Aenea steps out from the Sphinx.
The Church purportedly has a huge dislike of AIs and since Aenea is the daughter of an AI (the Keats cybrid) they are afraid of her (fearing her an agent of the TechnoCore) and so send their soldier Father Captain de Soya to capture her and bring her back to Pacem.
So, the first 90% of the story essentially is Aenea being chased across the galaxy by de Soya. She has a human, Raul Endymion (chosen by Martin Silenus, yes, he's still alive!), an android, A. Bettik (remember him from the first book?), and our old friend, the Shrike, as her protectors. The story literally takes us on a tour of the erstwhile WorldWeb. Aenea, along with Endymion, A. Bettik and the consul's Ship travels the worlds previously connected by the river Tethys as de Soya tracks her unsuccessfully, always just a step behind her. This part of the book is extremely slow and plodding.
As with 'Hyperion', 'Endymion' gets interesting right at the end. Simmons sets the stage for the final book with a series of revelations that promise a cracker of an ending to this wonderful saga. We learn that the Church that outwardly was against the creation of any AIs is infact in a Faustian pact with the TechnoCore. It was the core that gave the technology to tame the cruciforms to the Church. What we do not know is what the Core got in return! We know that the Church is about to launch a new crusade against the Ousters to obtain complete dominion over the galaxy. For this purpose they've created special soldiers. Machines capable of taking on the Shrike itself! We get a glimpse of sinister 'Peace and Justice' projects of the Church that leave entire worlds empty, worlds that refused to accept the cruciform!
Finally, we learn of "Something Else" from "Somewhere Else" that stole away the Earth before it could be destroyed by the TechnoCore, that activated the farcasters for Aenea, and that brought her to Earth for her apprenticeship to get her ready to fulfill her destiny.