"The Mystery Cruise" centers around best friends and impending business partners, Alvirah Meehan (Gail O'Grady), 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 Regan's 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 Nora's 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.