A TV movie continuing the adventures of the Love Boat gang.
Various passengers end up on board after receiving complimentary tickets from an agency called Luxury Travel, an outfit which turns out to be owned by famous reclusive billionaire Maxwell Thorn. Ace hypothesizes that Thorn plans to kill all the guests one by one, as in Agatha Christie's story "Ten Little Indians." But when Thorn is thrown overboard late one night, Ace figures events are shaping up more in the fashion of "Murder on the Orient Express." The Captain tells him he's seen too many movies.
Among the guests are an unmarried couple, Sarah York and Allan Davis, and Sarah's mother Jessica. Sarah and her mom want to strike a business deal with Thorn, which plan, of course, falls through when Thorn goes into the water.
Robert McBride, a former employee of Thorn with plenty to hide, is pursued by Margret Grant. But she comes to believe that McBride is the murderer, and calls off her pursuit. Another suspect is George Tillman, who survives an attempt on his life by poisoning. Thorn's loyal secretary, Irene Culver, grieves over the boss's passing, but somehow maintains a connection with a mysterious stranger who lurks continually in the background.
The Captain's wife, Emily, tries to liven things up on board ship by shaking up the normal routine, all the while solving the case without realizing she's doing it.