The Darkest Whisper by Gena Showalter (2009) is the fourth installment in her Lords of the Underworld series. If you enjoy paranormal romance and haven't read any of the Lords books yet, you're missing something wonderful.
You can also jump into the series at any point and not be lost. Yes, there's a continuing search for the recovery of Pandora's box and an ongoing battle between the Hunters and the Lords that moves through the books, and the Lords and their women, as they join the group, appear in each book. You won't be confused if you don't start at the first book, though, and Showalter does an excellent job of focusing primarily on the actual couple featured in the book.
Each immortal Lord is possessed by a demon released centuries ago when they opened Pandora's box and annoyed the gods. The Darkest Whisper is the story of Sabin, possessed by Doubt, and the lovely Gwendolyn (Gwen) the Timid, a very young Harpy. For the record, a timid Harpy is an oxymoron because they're the ultimate warriors. Keep in mind that Gwen is very young, though.
(And that's one of my favorite parts of Showalter's heroines; they are extremely strong and a central piece of the war against the Hunters. There's no lounging in safety a continent away while their men fight.)
Here's an excerpt from p.248-9, when Sabin is training Gwen to fight, and Kaia, Taliyah, and Bianka are Gwen's much older sisters:
Kaia's mouth hung open, as if she couldn't believe someone had spoken to her like that. Then she was stalking to him, murder in her gaze, nails bared, sharp teeth gleaming in the sunlight. "I'm going to snap your neck like a twig, demon."
"Bring it," he [Sabin] said, waving his fingers at her in a mocking salute.
An earsplitting squawk suddenly erupted from sweet little Gwen.
Both he and Kaia froze. Even Taliyah and Bianka stopped their sparring to face Gwen as she crouched, sights locked on her redheaded sister. The whites of her eyes had already turned black.
"Are you freaking kidding me?" Kaia gasped out. "I think she's going to attack me. What'd I do?"
"Threatened her man," Taliyah said coldly. "You knew better. I hope she claws her way to your spine."
Her man. Just the words had him rock hard, and it was freaking embarrassing. He couldn't allow her to hurt her sister. She'd never forgive herself. Sabin walked to Gwen, each step slow, measured. "Gwen, you will calm down. Understand?"
She snapped her teeth at him and almost nailed his chin. Only his quick reflexes saved him a severe biting. "Gwendolyn. That's wasn't very nice. Shall I bite you?"
Okay, now he was harder than a rock. "Well, I won't have anything to bite if you don't calm down."
Somehow, that reached her. She licked her lips, eyes fading to normal, body straightening. A tremor moved through her, and she swayed on her feet. He didn't touch her, not yet. He wouldn't want to stop and they had witnesses.
Although book three, The Darkest Pleasure, remains my favorite of the series so far, I think every book is a treasure.
My overall personal rating of The Darkest Whisper is a B+.