Jak Jinnaka is, at first sight, your typical John W. Campbell era Astounding SF hero: the capable man. Perhaps best popularised by Robert Heinlein in a series of early adult novels, the capable man is an archetype who can face up to everything the universe throws at him. Using his innate skills and intelligence he will not only overcome his myriad obstacles, but will change the world in the process. A slacker at heart (another touch of Heinlein's "lazy man" take on the capable man?), he has inadvertantly become a secret agent. Manipulated and "persuaded" he has completed one successful mission for his home habitat.
Jinnaka's universe is one where humanity made the leap to space in time to avoid extinction in a slower than light interstellar war, fought with relativistic weapons. It's a place where humanity is now a clade of civilisations and species, and a world where anarchy is kept at bay by aristocracy and tradition, wrapped up in the religious secularism of The Wager. Humanity and its one time enemies (now a refugee population on Pluto after humanity's secret weapon destroyed their star) are on trial for war crimes at a Galactic Court many light years away, and are waiting for a verdict which may mean extinction.
In A Princess Of The Aerie all is calm after the events of The Duke Of Uranium. Back at college after his succesful first mission, Jak and his buddies receive a message from his ex-girlfriend, now a Princess in another major habitat across the solar system. She needs him to come and deal with a problem. The powers that be see this as a solution to Jak's educational problems, and send him to her aid, as part of his junior task. But the message was (apparently) a fake, and Jak is enlisted in her royal guard (who'r role is more than, err, strictly ornamental). Conditioned to perform at her every whim, Jak finds himself caught up in palace intrigues that end with him heading to the downtrodden mining camps of Mercury while trying to avoid a persistent reporter and her swarm of robot cameras...
Despite it's superficial Campbellian air, this is most definately a modern adult novel. Barnes' themes here include corporate capitalism and its effects on societies, and non-senusal power imbalances in sexual relationships and their effects on the participants - as well as the role of mendacity in power politics. Barnes is writing an adventure yarn that happens to be a dissertation on misues of power. And one that works surprisingly effectively in either mode.
A Princes Of The Aerie turns the "Barnes Lite" mode on its head, producing a dark and intelligent story that throws a new light on what Barnes is doing with Jinnaka and his world. Now to wait for further revalations in In The Hall Of The Martian King.