“The Mystery Cruise” follows the adventures of close friends and soon-to-be business partners, Alvirah Meehan (played by Gail O’Grady), a lottery winner who has taken up amateur sleuthing, and Regan Reilly (portrayed by Michelle Harrison), a professional private investigator. After they save a wealthy socialite’s diamond-adorned dog (Carol Higgins Clark), the duo, along with their husbands, embark on a lavish three-day cruise around the San Juan Islands near Washington. They join Regan’s mother, Nora Reilly (Colleen Winton), a celebrated mystery novelist, who has organized a mystery game on the cruise to celebrate her new book’s launch. As the ship embarks on its journey, everyone eagerly assumes their roles in the game, with Alvirah particularly enthusiastic about her potential role as the “murderess.” However, the plot thickens when Alvirah suspects that a genuine murderer might be among them, prompting her and Regan to unravel the real-life mystery on the open sea.