Alvirah Meehan, lottery winner turned amateur sleuth, and private investigator Regan Reilly are guests, along with their spouses, on the "Santa Cruise." The cruise is a gift from Commodore Randolph Weed to a select group that "has made the world a better place." His largesse is prompted by the desire to create a buzz about his new cruise ship, the Royal Mermaid, as she sets out on her maiden voyage.

Alvirah, Regan, and her new husband, Jack -- head of the NYPD Major Case Squad -- are joined as guests on the cruise by a mystery fan convention celebrating a "ghost of honor," as well as ten men who donated time playing Santa Claus, now hoping for a restful post-season. That tranquility vanishes when two Santa suits disappear from a locked room, a storm develops, and an attempt is made on a passenger's life. As the Royal Mermaid sails through troubled waters, Alvirah, Regan, and Jack uncover clues that lead them to dangerous criminals not on the original guest list....