Sun of Suns — Karl Schroeder

It is the distant future. The world known as Virga is a fullerene balloon three thousand kilometers in diameter, filled with air, water, and aimlessly floating chunks of rock. The humans who live in this vast environment must build their own fusion suns and "towns" that are in the shape of enormous wood and rope wheels that are spun for gravity. Young, fit, bitter, and friendless, Hayden Griffin is a very dangerous man. He's come to the city of Rush in the nation of Slipstream with one thing in mind: to take murderous revenge for the deaths of his parents six years ago. His target is Admiral Chaison Fanning, head of the fleet of Slipstream, which conquered Hayden's nation of Aerie years ago. And the fact that Hayden's spent his adolescence living with pirates doesn't bode well for Fanning's chances . . .