Mystery on Maui — Carolyn Keene

NANCY RIDES A WAVE OF DANGER IN PURSUIT OF A SURFING SABOTEUR!
Nancy, Bess, and George are on Maui to check out a major international surfing competition. With its white sand, coconut palms, and beautiful blue sea, the setting is pure heaven. But there's trouble in paradise. Big money is at stake in the contest, and someone's playing a dirty game.

One of Nancy's surfer friends has received a death threat and could end up taking a permanent dive. And when Nancy plunges into the investigation, she lands in some very hot water. Now she's the number-one target, confronting new perils at every turn: treacherous riptides, poisonous snakes, and killer sharks!