Serpent's Reach - C.J. Cherryh
I picked this one up on a whim, knowing little other than the blurb on the back cover, which was all about revenge...

The setting for Serpent's Reach was even more interesting than I thought, since it's all about the relationship between humans who've been settled on this particular series of planets, way beyond the edge of what is otherwise explored space, and the insectoid hive-mind inhabitants of those planets. These particular humans are all but immortal, gatekeepers of the things the insectoids make, with humans of normal lifespans (the betas) and genetically-engineered servants to work for them.

Into this setting comes our protagonist, who is the only survivor of a major power play between clans. She is determined to have her revenge and does so, biding her time and then using the power and wealth given to her by her status to effectively destroy the whole system from within. It's a fascinating book, particularly in terms of the relationships between the different races and also those between those humans with vastly differing lifespans.