Murder walks the plank : a death on demand mystery / Carolyn Hart.

Enhanced descriptions from Syndetics:

It's "Corpse ahoy!" when death takes a pleasure cruise -- as we set sail once more with that incomparable, crime-solving duo, the Darlings.

Annie Darling, popular proprietress of the Death on Demand bookstore, has done it again! Her murder-mystery cruise in the waters off her not-always-idyllic isle of Broward's Rock is sure to be a roaring success, with every participant dressing up as a favorite fictional sleuth. And sure enough, everything goes swimmingly -- until one of the revelers plunges overboard. And despite hubby Max Darling's courageous rescue attempt, faux murder turns all too quickly into real-life death.

Over the next few days, the body count rises and Annie strongly suspects that all the victims were murdered most foully and that they are all connected in some unknown way. The trick now will be to prove it, with the able assistance of investigator-spouse Max, best friend and best customer Henny Brawley, local bestselling superstar Emma Lloyd, and even (surprise!) Annie's normally ditsy mother-in-law, Laurel.

But what the intrepid crime solvers do not realize is that the killer they seek is more ingeniously efficient than most -- and the puzzle they wish to solve is, in reality, a time bomb packed with an explosive mix of arson, assault, kidnapping, robbery . . . and homicide, of course. One false step and Annie and her canny cohorts will be blown off Broward's Rock for good . . . and they'll sink like stones into the cold, briny deep.