One of the very last Eberron novels published and in many ways the only true standalone novel, 'Lady Ruin' runs only 250 pages and does not make the best use of its brief time. 25 additional pages are given to the 'Abyssal Plague' prelude cross-over event, but as there's no sign of it having anything to do with Eberron I'm skipping it. Waggoner's 'Blade of the Flame' trilogy is strong writing, but I can't say the same here unfortunately.
A Karrnathi warlord sponsors a secret weapons-development scheme involving bonding soldiers with symbionts to create a powerful army. The problem is that symbionts are creations leftover from the Daelkyr War nine thousand years ago. Products of chaos, the symbionts are dangerous to their hosts and nearly-impossible to control.
Captain Lirra is second in command of the effort, working under her father and supervising her artificer uncle in his experiments to master these weapons. An experiment goes wrong...and Lirra is the only one strong enough to do what must be done to prevent A Daelkyr from crossing over into Eberron and remaking the world in its twisted vision.
Lirra is our primary viewpoint character with only the occasional visit to other officers in the Outland Guard and the baddies scheming to unleash chaos. The story make little attempt to follow a "party" structure, Lirra is mostly on her own, and Waggoner can't seem to carry the story without it. There was little time for development of character relations, so when we reach climactic fight scenes I didn't feel any attachment to the characters. The book's saving grace is the examination of how symbionts behave with hosts and several scenes of horror as people and monsters are molded like play-doh to suit the needs of the villain.