Horror mounts when a flu epidemic attacks Colorado Springs. Dr. Mike must attend the sick townspeople and protect others from getting the deadly disease. But being a lady doctor has people questioning whether she can handle the fatal epidemic.

A gunslinger (Johnny Cash) arrives looking for a quiet town in which to hang 'em up, but Colorado Springs is itching to lynch an immigrant (Christopher Keene Kelly) for cattle rustling to feed his starving family.

A bitter Loren, who blames Sully for his daughter's death, tries to repossess Dr. Mike's cabin when he learns he still owns the deed.

As Dr. Quinn is trying to persuade the townspeople that smallpox vaccinations are necessary, the father of Brain, Colleen, and Matthew arrives.

When several townspeople come down with mercury poisoning, Dr. Mike forces a reluctant Sully to guide her to the high mountain stream which may be the source of the problem. The trek is difficult for her, but she ultimately earns Sully's respect and gratitude after saving his life twice despite a broken wrist. Just as they confirm that the water is being polluted by a local mine owner whose mining process is dumping mercury into the stream, they are captured by his men. In the interim, worried townsfolk send out an inept posse to try to locate Sully and Dr. Mike. Olive backs Grace's new venture -- Grace's Cafe. In the end, Dr. Mike saves the day by curing the mine owner's son, who has fallen victim to the poisoned water, and convincing the owner to close the mine.