Dr. Mike (Jane Seymour) sends her children to stay at Sully's (Joe Lando) hideout while she battles a deadly diptheria epidemic that threatens the entire town.
Mike's mother (guest star Georgann Johnson) and sister, Rebecca (guest star Elinor Donahue), arrive for a Thanksgiving visit and refuse to leave, despite the epidemic. Their arrival leads to further friction between them and Mike's other sister, Marjorie (guest star Alley Mills), who becomes stricken herself.
As casualties mount, Dr. Mike butts heads with fellow doctor Andrew Cook (Brandon Douglas) about a new surgical procedure -- intubation.