Ransom of Tartarus

There's a traitor on the planet Tartarus!

With the insider's aid, Dar-kan hira-Gurd -- the beautiful, sadistic, dangerous Ghendarian commander -- invades the City of the Ruler. She usurps the throne of Ahn-eld, then plots her long-awaited revenge upon Malkis of Tartarus.

Acting on a gut instinct that the planet is under attack, Richard Hughes, commander of Astrella II, risks battling Ghendarian warships in a desperate attempt to rescue Malkis and Rona. But in order to save his wife, his world, and his friends from the brutal and merciless invaders, Malkis is forced to make an unthinkable sacrifice!
Ransom of Tartarus is the third book in the Tartarus Trilogy. Books one and two of the trilogy are Judgment on Tartarus and True Son of Tartarus.