Willow's Windfall — C.B. Samet

She's a medium. He's a skeptic. A hidden treasure leads them on a dangerous adventure. 

Willow Nightingale helps ghosts cross into the spirit world. She accepts the task to rid Mark Stryker of the spirit haunting his house, but they discover the ghost is linked to a three-hundred-year-old pirate treasure. When Willow and Mark race to find it, they discover they aren't the only ones after it. They must rely on each other and the ghost of a pirate if they're going to survive.