Death Rides the Surf — Nora Charles

Once a snowbird, now full-time resident and sometime sleuth Kate Kennedy “is a stylish and sophisticated Miss Marple, seeking justice in sunny South Florida instead of a rainy English Village, and meeting the most delightfully eccentric suspects in the process.” (Victoria Thompson, author of Murder in Chinatown)
 
Tired of college, Kate Kennedy's granddaughter, Katherine, drops out and heads for Florida, landing in the apartment of Kate's best friend. In her quest for a new life, she takes up with a gang of surfers that go by name “The Four Boardsmen of the Apocalypse.”
 
But catching waves can be a dangerous pastime. When Katherine's surfer crush is killed in a shark attack, foul play is suspected, especially by the police. Fingers are pointing at Katherine -- including, to Kate's disappointment, that of her friend Detective Nick Carbone. It's up to Kate to prove her beloved granddaughter's innocence or else Katherine's “new life” will be spent behind bars.