Xerus: loyal, protective, swift, powerful. Named predomis—highest warrior among the vrisha—and guardian to his queen. And Lana's one true mate. Several years after Lazris, Lana has called the vrisha's world her home. After a long mission kept her and Xerus away, they finally return to Tryth, hoping to settle back into the life they had and spend each moment together. When the discovery of a galaxy-sized threat presents itself, and they learn of a dangerous empire seeking to hunt humans for its benefit, Lana and Xerus must work together to stop a major catastrophe and possible war before it's too late. As large of a problem as that seems, Lana finds an even darker, more disturbing complication within her own mate. Something that could sever their relationship completely and shatter the bond they had built since the beginning. As they strive to save the human race from being hunted and killed, Lana fights to save the one who matters to her the most. _Heart's Keeper _is the fourth book in the Dark World Mates series. Intended for mature listeners.