This is a remarkable bit of world-building, a concept that's hard to swallow at first but is presented carefully and consistently and ends up making sense both as something that could work and something that would be worth building (since it's an artificial world). We get some interesting societies populating the bit of the world we see, and some interesting characters and development, and plenty of high adventure with things blowing up, people dying gallantly, and beautiful women. It's a great book up to the end, where just when we think we see a nice, satisfying ending, things go to hell, and if things are really the way we're being told they are, it's hard to see where there's room for the story to continue, despite the fact that it says "Book one of Virga" on the cover.
Fabulous setting, great action, decent characters, loved it until the ending that, while maybe not ruining it, certainly damaged it. 8 out of 10.
**** PLOT SUMMARY -- MASSIVE SPOILERS ****
The world Virga is an amazing conceit: a planet-sized bubble of air with small fusion powered "suns" which power a water cycle and an ecology including humans, who build free-fall cities out of wood and get around using jet engines.
We first meet Hayden Griffin as a kid living in the nation of Aerie. Aerie is small and weak because it doesn't have its own sun. His mother is part of a team working in secret to build one. Slipstream, a powerful nation based on a small asteroid that orbits through the bubble of Virga, is currently passing through. Slipstream doesn't want one of its client states gaining the power to break away, so they attack the new sun, kill Hayden's mother, and send him spinning off into exile.
We catch up with Hayden a few years later, where he's wound up in Slipstream with a personal mission to avenge his mother's death by killing Admiral Fanning, the commander of record of the strike force that killed his mother. He gets himself assigned as a chauffeur for Fanning's wife Venera, an intriguer who would give Lucretia Borgia a run for her money. He gets one chance at being close to Fanning, but doesn't have the guts to kill him. Venera has a secret spy network which gets pictures of a military development by the Falcon Formation, a very powerful and repressive kingdom which Slipstream and Aerie are moving into. Hayden gets a look at a picture he's not supposed to see and uses his knowledge of flying to provide valuable analysis. Venera convinces Fanning that the secret force is the real threat, but the Pilot (king) of Slipstream doesn't believe it and means to send the whole navy to crush a smaller upstart. Fanning is convinced that that uprising is just a diversion. Aubri Muhallan is another mysterious woman; she turns out not to be native to Virga at all, and knows things about the technology that nobody else does. Hayden falls in love with her. Between Venera and Aubri, Fanning has the pieces for a wild, unauthorized scheme to try to destroy the Falcon fleet and save his nation. He takes a small fleet, 6 old, unimportant ships, off on the quest. They battle a pirate fleet near the icy outside wall of Virga; the pirates are actually some of Hayden's former countrymen of Aerie, but Hayden, though conflicted, manages to realize that if Falcon wins, Aerie will be worse off than it ever was as Slipstream's client. He uses his initiative to knock some icebergs loose from the skin which wreck the pirate fleet. Next they arrive at the Visitor's Station, the point of contact with the outside world, and reclaim an artifact which is supposed to be a map to a long-lost pirate hoard. The reason it matters is that in the hoard there is supposed to be a Key which will allow Aubri to enter Candesce, the main sun at the center of Virga, and turn off its jamming radiation, which in turn will allow the radar she's built for the fleet to work. The fleet works its way inward, but the kingdom of Gehellen considers them barbarians and doesn't let them pass willingly. Through bluff and causing a diplomatic outrage, they manage to pass through to Leaf's Choir, a huge free-fall forest which burned hundreds of years ago, creating a huge stable oxygen-free zone called a sargasso. The real nature of Fanning's fleet is now clear -- it's meant to be able to operate here. The map is good; they find the treasure. Hayden, Venera, Aubri, and Venera's sociopath bodygard Lyle Carrier are sent off on their own to turn off Candesce's defenses while the fleet goes to track down the secret Falcon force.
At Candesce, Hayden has his own agenda: he wants to get the parts to build another sun. Carrier, it turns out, is the nasty guy he is today because he murdered his own son for being part of Aerie's old sun plot. Carrier tries to kill Hayden; Hayden prevails and kills him instead. Aubri disables the sun, but then refuses to re-enable it; her secret mission was to leave the defenses turned off so the pervasive nanotech reality outside of Virga, Artificial Nature, can take over. Aubri hates Artificial Nature but did it anyway because she has an assassin built into her body that will kill her if she doesn't cooperate. Venera kills Aubri for her betrayal; Aubri appears to be trying to turn the defenses back on at the end but doesn't have the strength. Hayden drops her body into the suns that are turning on and allows Venera to hitch a ride on his stash of sun components to escape the heat. Venera jumps off as soon as they're out of the heat. It's unclear where either of them are going to end up, and if what Aubri told Hayden about Artificial Nature is true, it's all irrelevant because Artificial Nature is now going to invade and eat Virga.