U is for Undertow is the twenty-first in the Kinsey Millhone mystery series by Sue Grafton.

In 1960s Santa Teresa, California, a child is kidnapped and never returned . . .

When the case is reopened after twenty years, a man - Michael Sutton - contacts private detective Kinsey Millhone for help. He claims to have recalled a strange and disturbing memory which just might provide the key to the mystery. He may have stumbled across the kidnappers burying Mary Claire Fitzhugh's body . . .

But Michael's account is indistinct - he was only six years old at the time of the kidnapping; and even members of his family try to discredit his evidence. But Kinsey is certain there is something vital within Michael's recollections. And even when what is eventually unearthed isn't what anyone expected, she can't quite let go of the case.

As Kinsey gradually brings to light the stories of the protagonists involved in the tragedy, from Country Club parents to their free-living, hippy children, the truth finally begins to emerge. And while stepping back into the past, Kinsey discovers more about her own history too . . .