Voyage Into Twilight — Sandra C. Stixrude

Commander Romenel Devar fears nothing--except sleep. Something creeps out of his nightmares and tries to drain the life from him. His search for help will lead him to strange lands, voices from a distant past, and answers he doesn't want.

Something is hunting mercenary commander Romenel Devar, a monster disguised as friends and loved ones, so he can't even describe it. He knows it's slowly killing him, though, and he desperately needs help.

Marya and Roke have retired to their house on the steppes, their lives finally peaceful and uneventful. When Romenel collapses on their front doorstep, Marya reminds her husband that no one retires from being a hero.

Their journey takes them to the other side of the world where hordes of monsters lurk and the rules of society are turned on their heads. Romenel needs to understand both this strange new world and the hints from a distant, shared past to unravel the means to stop the monsters' deadly hunts.