"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.