Descending Into Darkness by Alainna MacPherson

Jessandra was content with her life in New York, before a creature hunted her down and took her down to an underworld beneath the city. There, he reveals that she’s more than just a waitress living in a walk-up apartment with her sister. She’s his people’s last hope in ever seeing freedom.

Fallon’s people are done being slaves. Lacking the numbers to simply fight back and rebel, they’ve found a secret weapon: Jessandra. Once she discovers all that she is and can be, they will have a fighting chance.

That’s if they can keep their hands off one another. Should the enemy find out about Jessandra, the whole plan goes to hell. And her cover relies on the two keeping the heat between them a secret.