Skinny Dip by Carl Hiassen

Joey Perone is pushed off a cruise ship by her husband on her first anniversary. Only her skill and training as a collegiate diver allow her to survive the fall and the hundreds of miles of ocean before she is rescued off a small island near Florida by retired police investigator Mick Stranahan. Chaz Perone plays the grieving widower well until he gets too wrapped up with his mistress, the goon sent by his 'boss' to make sure his investment stays safe, and his real job as a biologist testing nitrate runoff in the Everglades. Joey gets Mick to help her mess with Chaz and let him think he's being blackmailed and with pressure coming from the mistress, the 'by the book' cop, the 'blackmailer', the goon, and the 'boss', Chaz self-destructs and Joey sits back to watch. The grand finale, though, has one wondering if the ends justified the means