The Once and Future Queen — Marilynn Byerly

Immortals are a race so illusive most believe them a fairy tale of space. Many tales differ, but all declare them the most deadly race in the universe with a technology beyond imagining and physical abilities beyond belief. With powers so vast, they have paid little attention to humanity. Until now. Xenda, a human colony of royalty, castles, and courtly lifestyle, was a quiet pastoral world until the arrival of two Immortal women who vied for the love of the planet's king. But before they left, he was dead, and the planet and its people were ravaged by invaders. Peace came with the defeat of evil Fionna by Dia, but now Fionna is back, and Dia is dead. To save this world, Col. Val Grant and his crew of the finest minds in the galaxy face an enemy who cannot be beaten.