In this episode, Jessica accompanies her niece, Pamela (Belinda Montgomery) on a cruise...and viewers KNOW that sooner or later, someone is going to die on this boat! In fact, wherever Jessica goes (such as Hollywood, to Broadway or to visit family), you know that death follows!
Pamela is a very sad young lady. Following her husband's death, she had a nervous breakdown and is an emotional mess. Once on the cruise, someone begins harassing her...leaving her notes from her dead husband, hearing the husband's voice, etcetera. However, very soon Jessica also sees and hears these things, so you know SOMEONE is trying to drive Pamela over the edge....but why?
While the show has some serious overacting (even Angela Lansbury does this in this particular episode), the show is a neat one because the crime is so unusual. Well worth seeing.
By the way, I think casting Leslie Nielsen as the ship's captain was an inside joke. After all, he also played the captain in the ill-fated "Poseidon Adventure"!