U is for Undertow by Sue Grafton

Kinsey Millhone is hired to help Michael Sutton find the place where he is afraid a body may be buried. She also has an invitation to a family get-together, which she really doesn't want to go to. Kinsey convinces the police to dig up a body all right, but it isn't what they expected to find. Lots of twists and turns for an interesting mystery. Sandy Penton