City on Fire by Walter Jon Williams
Aiah worked for the Plasm Authority, metering the shimmering substance that powered the world-city, until she fell in love with Constantine, the rebel Metropolitan fighting a war to overthrow the corrupt dynasty of the Keremaths.
Now the war is over, and Aiah is at the mercy of Constantine, the tyrant she created. As sexually irresistible as ever, the former rebel has a new job for Aiah: track down the outlaw plasm divers of Caraqui and recruit them to help destroy the Silver Hand, a murderous remnant of the old kleptocracy. A reluctant Aiah finds herself working with a horrifying ally the "hanged man," Taikoen, a once-human monster that lives in the plasm well, leaving it only to kill. But for Aiah, there can be no turning back. Constantine's war against the Handmen will put Aiah in touch with her lost Barkazil heritage. And it may allow her to get a glimpse of heaven itself, and to discover what waits beyond the Shield.