D is for Deadbeat by Sue Grafton

When Alvin Limardo walks into P.I. Kinsey Millhone's office, she smells bad news. He wants Kinsey to deliver a cashier's check for $25,000. The recipient: a fifteen-year-old boy. It's a simple matter. So simple that Kinsey wonders why he doesn't deliver the money himself. She's almost certain something is off. But with rent due, Kinsey accepts Limardo's retainer against her better judgment…

Limardo pays her with another check as the retainer. It bounces and Kinsey discovers she's been had. She learns that he is really John Daggett—an ex-con with a drinking problem, two wives to boot, and a slew of people who would like to see him dead. Kinsey is out $400 and she's now in hot pursuit of Daggett.

When Daggett's corpse shows up floating in the Santa Teresa surf, the cops rule it an accident. Kinsey thinks it's murder. But seeking justice for a man who everyone seemed to despise is a lot tougher than she bargained for—and what awaits her at the end of the road is much more disturbing than she could've ever imagined.