"Diagnosis Murder," a lighthearted mystery drama, revolves around Dr. Mark Sloan (Dick Van Dyke), a teaching physician who also becomes deeply involved in crime-solving in his role as consultant to the local police department. He is a widower who lives in a beach house, where a frequent visitor is his policeman son, Steve (Barry Van Dyke). Assisting him, both medically and as occasional investigators, are Amanda Bentley (Victoria Rowell), a pathologist, and Dr. Jesse Travis (Charlie Schlatter), an enthusiastic young resident doctor. A minor irritant is Norman Briggs (Michael Tucci), the tightfisted but hapless hospital administrator.
"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.
