The Naked Truth by Natasha Rostova
Callie's marriage to Logan Waterford - one of the Savannah's wealthiest citizens - has left her feeling confined and unfulfilled. Logan is too cold, too remote, and too repressed. One day she leaves him, then hides out at her sister's place, determined to change her life and explore her sexual and spiritual side.
But Logan's too proud to accept the situation. He's determined to get her back, and hires a private detective. While Callie is becoming immersed in the wild southern sensuality of voodoo practices, the secrets Logan is about to reveal are darker and more strangely erotic than anything Callie's prepared for.