NIGHTMASTER (4) by Susan Krinard: When Trinity Ward — an Aegis agent who is half vampire, half human — agrees to travel as a slave to the Opir city of Erebus to spy on the human enemy, she may have taken on more than she can handle. After being fought over by two Bloodmasters, she becomes the slave of an Opir male named Lord Ares, who has a better reputation than most. She sets out to seduce Ares to gain information, but she quickly succumbs to her attraction for him. The mythology of the war between humans and the Opir race and their bloodslaves makes for an interesting storyline. Nightmaster combines great sexual tension and almost non-stop action.