In a story based on the then-recent outbreak of Legionnaire's Disease, a mysterious illness strikes dozens of guests at a Lake Tahoe resort where Quincy and Lee are attending a forensic investigator's convention. Quincy continues to work with the doctors in Lake Tahoe to determine the cause of the mysterious illness that has killed or sickened dozens of guests, and it turns out the murderer was one of their own. Van Johnson, Buddy Hackett, and Jo Ann Pflug guest star.

NOTE: This was the first two-hour episode of the series. It was divided into two parts for syndication.

Quincy and a group of medical school students work on a cold murder case after they find a femur bone with a gunshot mark at a construction site. Fred Grandy appears as a student. (Note: This episode marks the final appearance of Lynette Mettey as Lee, Quincy's girlfriend, and the final episode as part of the NBC Mystery Movie series).

Quincy's and Danny's fishing trip in the town of Paradise turns into a murder investigation which some members of the town, including the sheriff (Pernell Roberts) tries to prevent Quincy from working on. Jack Kelly guest stars and Jamie Lee Curtis made her acting debut as a girl in a changing room that Quincy opened by mistake looking for someone else.

A death investigation in a refinery fire brings Quincy into conflict with his former pathology professor and mentor who now has become a witness-for-hire.

Quincy has to find out who was responsible for a hit-and-run accident at Danny's place, but there are some government officials who would rather keep the person's identity secret.

Quincy is nowhere to be found when a corpse brought into the morgue isn't as dead as believed, Monahan investigates a diamond smuggling case, and a boy with unique symptoms arrives at the hospital. Bob Crane, Yuki Shimoda, and Louise Sorel guest star.

NOTE: Jack Klugman does not appear in the episode (for the only time in the series) because he disliked the script, and the incident began the process of Glen A. Larson leaving the show at the end of the season.

Dr. Astin's wife picks up a hitchhiking child and is involved in an auto accident; however, Quincy determines some of the boy's injuries occurred before the crash, and he immediately suspects the parents of child abuse.

A university medical student uncovers evidence (including a hot dog) that a body donated to the university was actually a murder victim.

The unusual cause of death of an auto accident victim results in the arrest of an innocent man, and Quincy attempts to clear his name by investigating the source of radiation exposure the victim received before his death.

A politically active priest is found dead of natural causes in the bed of a prostitute, and Quincy attempts to find out how he got there. Joseph Campanella and John Saxon guest star.

People are dying of heart problems at Valleyview Sanitarium, except the deceased had no heart problems, and this leads Quincy to search for a potential "Angel of Death" inside the well-respected facility. Carolyn Jones guest stars.

A series of rapes in Los Angeles results in the death of a nurse. Quincy and Monahan search for the rapist, but the investigation is hindered by an incompetent doctor and nurse. The case becomes personal to Quincy when the rapist attacks a rape counselor the coroner has gotten close to. Adrienne Barbeau and Kim Cattrall guest star.