The Devil Laughed

Moriah Dru, owner of Child Trace, and her lover, Richard Lake, an Atlanta police lieutenant, have been invited to Lake Lanier in the mountains of North Georgia for the scorcher of a 4th of July holiday. There, Dru discovers the stern of a long-missing boat protruding from the waters in a cove.
Two couples were partying onboard when the sailboat disappeared. Evangeline, a 13-year old prodigy, wants to hire Dru to find her mother.
Dru discovered the sailboat, and the juvenile judge is a friend, so she takes the case. Now, she's reversing her method of operation — working for a child to find an adult.