Don't Drink the Water — Susan Rogers Cooper

There is no love lost between novelist/sometime sleuth E.J. Pugh and her three sisters: four high-strung Texas redheads who have made sibling rivalry an art form. In an attempt to ease their stretched-thin family ties, the ladies and their respective mates have rented a vacation home together on the Caribbean island of St. John. But reconciliation must take a back seat to crim detection when a waterlogged corpse is discovered clogging up the cistern of their stunning beachfront house.

The body belongs to a former employee of the dentist husband of sister Liz, which leads the local police captain to surmise that the killer is a member of the clan--especially after an exploding count up from one. E.J., however, is not convinced. And, to the chagrin of her loving, long-suffering hubby, Willis, she's determined to salvage what's left of their vacation by exposing whomever is rapidly turning a family gathering into a wake in paradise.