The Mystery Cruise centers around best friends and impending business partners, Alvirah Meehan (Gail OGrady), a lottery winner turned amateur sleuth, and Regan Reilly (Michelle Harrison), a private investigator. After rescuing the diamond-collared pooch of a wealthy socialite (Carol Higgins Clark), the two heroines set off with their spouses to join Regans mom, Nora Reilly (Colleen Winton), a world famous mystery writer, on a luxurious three day cruise around the San Juan Island off the coast of Washington. The cruise serves as the setting for a mystery game created to promote the release of Noras latest book. As the boat calmly sets sail, everyone is enjoying getting into character, especially Alvirah, who may or may not be the games murderess. But troubled waters lie ahead when Alvirah gets a hunch that a real killer may be on board and, together with Regan, the pair teams up to solve the high seas whodunnit.