U is for Undertow by Sue Grafton

Private detective Kinsey Millhone is hired by Michael Sutton to find out if something he has just remembered from his childhood really happened. When he was six in 1967, he remembers being in a neighbor's backyard and seeing two men burying something. He feels it was the body of Mary Claire Fitzhugh who was kidnapped back then and never found. Now in 1988, he hopes Kinsey can find the grave and the men. Alternating back and forth between the past and present (as well as the points of view of Kinsey and other characters possibly integral to the crime), Grafton has written a more complex mystery than some of her earlier books in the series. It was an enjoyable read.