NOTE: Even if you're not interested in the Posleen, or science fiction in general, this book is still worth picking up just for the afterword, which is about...let's call it "pragmatics of religion".
That teaser aside, the Tuloriad is the story of a Posleen god-king who, with the help of an Indowy, leads his people away from Earth to a safer place. Some of the story is about the history of the Posleen, which is interesting; some of it is setting up the Climactic Battle, which I thought was a bit contrived--where "a bit" means "roughly 99%". I suspect that there was a story conference along these lines:
Kratman: "Hey John, listen to what [historical figure's name would be a spoiler] did!"
Ringo: "Yeah, that's pretty hardcore."
Kratman: "It would be cool if we could work that into this."
Ringo: "Posleen wouldn't normally do that, but maybe if...but we'd have to have someone using pikes."
Kratman: "Don't the Swiss Guards still have halberds?"
Ringo: [locks himself in a freezer and cranks out 40,000 words in a day].
If you've read all the other Legacy of the Aldenata books, you will of course read this one too. If you haven't, this isn't the place to start. But do read the Afterword.