Tall, Dark & Horny by Rochelle Paige

Adan Deville had ruled The Abyss for centuries. The powerful demon enforced his laws with an iron fist, and no one dared test him…until a delicate human wandered into his domain.
Calliope Ash didn’t plan to stumble across a supernatural hotel in the middle of a storm. All she wanted was to salvage a ruined travel itinerary. Then she locked eyes with a man who made her heart forget how to beat—and discovered there was more to this world than she ever knew. Including herself.=