When Sly Harrell sets out to find a cabin cruiser to entertain his new girlfriend, he finds them expensive and buying one full of possible regrets. The boat broker suggests renting or borrowing a vessel for a trial trip so Sly can be sure of what he really wants. The process of finding a boat to borrow sets off a series of events that ends in his frantic effort to save 10,000 people.
After finding how difficult and expensive renting a large cruiser would be, Sly checks with Riaffort Richards (Sly's lawyer) to see if he knows someone who has a boat they're willing to loan or rent reasonably. Sly's need for a boat coincides with Richards need to get out of a commitment to one of his clients. Sly meets with the lawyer's client, Melanie Hellman. He agrees to "chaperone" a four- day trial run to determine if Hellman's 30-year-old daughter is trustworthy enough to use the boat, the Nancy Lynn. The plan: a month cruising the Caribbean with her boyfriend and two other couples. In return, Sly will get the use of the boat for a week.
The brief cruise proves to be revealing in a most negative way. Sly finds the daughter unable to manage herself, much less any type of an endeavor. He counsels against letting the girl have the boat and decides to turn down the opportunity for $50,000 to accompany the three couples on the trip. Unwisely, Melanie decides to let the daughter take the boat anyway, believing since the boat will be captained by her employee, things will be alright.
Sly finds and rents another boat. He's on a "trial" cruise with his girlfriend and Trotter (and girlfriend) when he's contacted by his lawyer friend. The Nancy Lynn has disappeared after two and a half weeks at sea. He cuts his trip short and accepts Melanie's frantic offer of $250,000 to locate the Nancy Lynn and her daughter.
When Sly begins to have his agents, Russ and Val Foxx, investigate the backgrounds of the couples accompanying the daughter and boyfriend, one alarming fact after another is uncovered. The identities are false. One couple "does not exist" and the other has a sinister past. So does the daughter's boyfriend.
Sly uncovers possible connections to human trafficking...drug smuggling...and terrorism. Which one is it? Are all involved? The local governments become interested after delays. In the midst of uncovering these disturbing facts, a seemingly reassuring message from the boat's captain is received. However, when Sly examines the telex more carefully, he is alarmed to find a coded distress call in the text.
It becomes a race to trace the Nancy Lynn's path to several ports where they pick up components to make a lethal weapon. This becomes more difficult when governmental officials lose interest after the reassuring message is disclosed and believed.
Time ticks by, and Sly's efforts finally uncover the plot's objectives and deadly intent. The components for six torpedoes and the means to launch them have been gathered and the Nancy Lynn is being converted to a torpedo boat. The problem: the last pieces of the mystery aren't placed together until four hours before the attack. Two cruise ships will be within a few miles apart and will be attacked in sequence with the possibility of killing 10,000 passengers.
Sly and his "crew" race to try to stop the attack...with a cabin cruiser and make-shift armaments. Can they save the cruise ships, the Nancy Lynn, and those few good people on it?