This is yet another great concept, but is filled with glaring plot-holes.
The story begins with a prologue set in the times of the Crusades, where a lone surviving knight of one of history's bloodiest sieges was held between King Richard and Saladin, wakes up all alone on a battlefield. Essentially, its a Chariots of the Gods moment, just not done with as much excitement as it could have been.
Then the story jumps forward in time, where Domi and Mariah Falk are deep in the jungles of Brazil. Domi is way too relaxed walking among with 'bare feet' in an area that is rife with potentially dangerous animals, snakes, etc... That quickly, the tension is bled away from the get-go.
After Domi and Mariah uncover a hidden spaceship, an unknown craft shows up and snatches it out of the ground - with Domi trapped inside. (What a timely coincidence!)
Basically, this story is about a hidden race of beings who live in their glittering city located in a quantum rift, who have been stealing alien tech for countless centuries.
So, right away, I can't help but think: Where have they been this entire series when the Cerberus team have been uncovering - and using! - alien tech for nearly 70 books?
Then, in a seemingly half-cocked plan, Grant and Kane don't even argue this plan, which is hatched by Lakesh - to have Grant and Kane do a mock battle with their Mantas above the area of Domi's kidnapping. All that came off half-contrived, placing Grant in mortal danger without knowing for sure if this ploy would even work or not. But of course it does. (But they have been flying the Mantas for years, from Earth to the Moon, so why didn't this 'hidden race' notice them then?
The whole problem in this book is that everyone was so darn RELAXED. No tension. From what could have and should have been a dangerous outing in the wilds of Brazil, to Kane, Brigid, and Grant first entering this airborne city that they've never been to, searching for their kidnapped friend, but asking NO questions of their captors. And when they finally do, it feels way too late.
With all due respect to Rik Hoskin, this was another book that held much potential, but needed that explanation of these high-tech race of people having never noticed the Cerberus team in all this time.