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.

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.

Dr. Mike takes in Red McCall, a down-and-out cowboy, and his ailing half-breed infant child. McCall reaches the end of his rope trying to care for his baby, so after robbing Loren's store, he leaves the baby in Michaela's care, sensing she could find a suitable home for his child. Dr. Mike's attempts to find a home for the baby prove futile.

When she travels to a remote cabin to check on the health of it's owner, she finds him badly mangled from a bear attack. Her horse is frightened off by the bear, and she's marooned in the cabin until Sully shows up looking for her. They narrowly escape being the rabid bear's next victims.

After returning to town, Dr. Mike decides she'd rather raise the child herself than turn him over to an orphanage. However, Sully locates Red and convinces him to keep the child.

After ambushing Black Kettle's camp, General Custer enters the town carrying wounded soldiers and Indian prisoners, including Cloud Dancing, whom Custer threatens to kill if Dr. Mike does not treat his men before the injured braves.

Later, Dr. Mike treats Cloud Dancing's broken arm while he remains shackled in the livery after Custer's interrogation. When Custer jokingly hauls Cloud Dancing before a firing squad that fires blanks, Dr. Mike and Sully engineer Cloud Dancing's escape.

Meanwhile, Olive opens a Hurdy Gurdy, recruiting girls from the immigrant camp and a reluctant Loren, Horace and Jake for the band. Matthew buys all of Ingrid's dance tickets then shyly confesses that he doesn't know how to dance. Robert E. and Grace exchange looks. Robert E. is still burned from The Visitor (#3).

After a patient of Dr. Mike's dies of blood poisoning, she accuses Jake, the barber, of infecting the man with his dirty razor. Her accusation throws Jake into an alcoholic binge. Dr. Mike tries in vain to pull him out of it, but finally realizes he must be the one to want to stop drinking. She gives him something to live for by pointing out his many friends in town, including her.

Meanwhile, Mike's children try to help her deal with her loneliness on her 35th birthday by conspiring to find her a proper suitor before her surprise party

Matthew's sudden announcement that he wants to marry Ingrid causes upheaval in his relationship with Dr. Mike, who feels he's too young. In an effort to prove he's man enough to make his own decisions, he convinces Sully and Cloud Dancing to allow him to partake in a four-day Cheyenne ritual. This is the final straw for Dr. Mike, and she confronts Sully before she storms off looking for Matthew.

Meanwhile, Ingrid suffers asthma attacks, and her treatment is undermined by Dr. Mike's disapproval of their marriage plans. Dr. Mike comes upon Matthew going through the rite of passage and seeming at peace with himself, so she lets him finish uninterrupted.

Later, Dr. Mike and Matthew resolve their differences, with him deciding to delay the wedding and her giving Matthew her engagement ring for Ingrid.

David Watkins, a civil war photographer arrives in Colorado Springs. Dr. Mike diagnoses David's diabetes and is frustrated that he refuses treatment and will ultimately go blind. David suggests taking a portrait of the town and an argument ensues over who will be in it. When the camera equipment is destroyed, the whole town must pull together to create a camera and take the photo before David's eyesight fails.

At the same time, Mrs. Bing, Horace's mother, is brought to town, seriously ill. Mrs. Bing disapproves of Myra until she learns how much they love each other, and on her deathbed bestows her blessing on their marriage.

After Snowbird gives Mike an Indian pony, Flash, in thanks for her work at the reservation Mike tries to enter the Territory Stakes Race, but race officials, Loren and Jake, won't allow a woman to ride. Dr. Cassidy arrives from Denver with his champion horse and spurns Mike attempts to speak to him colleague to colleague. Dr. Cassidy's rider, Drew, is injured and Mike diagnoses cranial compression, yet Dr. Cassidy refuses Mike's assistance. Drew dies and an angry Mike is determined to enter the race, disguised as a man. Meanwhile, with encouragement from Grace, Brian enters a pie-baking contest and is met with skepticism from Colleen and Loren. To everyone's surprise, Brian is declared the winner. Mike rides the race of her life and wins, but is disqualified when her disguise is revealed and Hank, riding Dr. Cassidy's horse, is declared the winner.

Halloween is trick-or-treat for the residents of Colorado Springs when Sully's dead wife, Abigail, haunts Dr. Mike, after Sully suggests fixing up the homestead for her. Eventually, Mike is able to lay Abigail's ghost to rest. Meanwhile, Brian becomes terrified after his investigations lead him to believe Dorothy is a witch. But, later she helps him deal with his sadness about the fading memory of his mother. Jake and Loren's prank on the town backfires when Jake pronounces a man dead and his ""corpse"" walks away -- Mike later diagnoses the man as a catalepsy sufferer.

Mike receives an emergency telegram from her sister Rebecca -- her mother is gravely ill. Mike rushes to Boston to her mother's side, the Cooper kids in tow, where Dr. Mike and her ""roughhewn"" children are met with raised eyebrows by Dr. Quinn's own family. While consulting with Elizabeth Quinn's attending physician, Dr. Mike meets a handsome and progressive Doctor, Dr. William Burke. Dr. Mike's prognosis of her mother (hepatitis) differs with Mrs. Quinn's doctor, Dr. Hanson, who diagnoses cancer. Dr. Burke, however, believes Dr. Mike may be onto something. They have a lot in common and develop a strong mutual admiration for each other. They work together to cure Mrs. Quinn and some of Dr. Burke's other patients. Meanwhile, Matthew chafes at being stuck in Boston away from Ingrid, while Colleen appreciates the learned and cultured atmosphere and Brian adores the candy stores. Just when everyone has settled comfortably into the Boston routine, Sully shows up, unannounced and in buckskin

Sully arrives in Boston and discovers that he's facing worthy competition for Mike's affection in the form of Dr. William Burke. Sully at first settles uncomfortably into Mike's Boston surroundings, but later, with prodding from the kids, submits to a grand makeover. Later, Sully romances Mike with dining and dancing, even attending an opera together. At an all-male medical society, Dr. Burke steps aside so that Mike can present a paper on Indian medicine, while Sully looks on. Afterward, Sully overhears Dr. Burke proposing marriage to Mike and heads back to Colorado, but not before confessing his love to Mike. In the end, Mike declines Dr. Burke's marriage proposal and Mike and the kids return to Colorado, where Dr. Mike returns Sully's declaration of love with a vow in kind.

Mike is called away to Soda Springs to help with an outbreak of influenza and Sully promises to stay with the children. Sully plays ""Mr. Mom"" but the kids grow restless. While out exploring caves with Brian, Sully is shot trying to intervene between the Indians and the cavalry. When the smoke clears, Brian can't locate Sully and goes to town for help. The Reverend helps the kids hide Sully, who now has a bounty on his head. They take Sully to the cave for safety. Colleen enlists the Reverend's help to bring supplies from the clinic, but he is spotted by Hank and Jake, who are out for the bounty. They knock Hank out and tie him up, but when Colleen is forced to remove the bullet, she must employ Jake's assistance to save Sully's life. When finally they ride back into town, the Cavalry tries to arrest Sully for blowing up the railroad, but the townsfolk provide Sully with an alibi preventing his arrest.

Miners gather in front of Loren Bray's store to protest Loren's not extending credit to striking miners, and for doing business with the mine owners. A budding union leader, Conrad, is there trying to organize the workers. At the same time, Travis Stone, the mining boss, rides up, hands out flyers advertising for scabs. An angry miner throws a stick of dynamite onto Loren's porch, which Sully, who gets knocked out in the subsequent fray, comes to just soon enough to put out. Matthew takes a flyer -- decides he'll take the job to augment building costs on his homestead. By doing this, he's at cross-purposes with Sully and Mike, who try to talk him out of it.

Grace tells Loren she won't be buying anything from him until the strike's over, due to his unfair trade practices with the striking miners. Matthew finds, to his dismay, that Loren charges 10 cents on every dollar of ""scrip"" (miner's credit) for ""bookkeeping"" costs. Later, as Mike administers some bicarbonate of soda (Brian's got a

Catherine, a beautiful blond woman captured by and raised with renegade Indians, is brought to Colorado Springs by soldiers when her tribe, which includes her husband, is wiped out, leaving her the sole survivor. She initially earns the townsfolks' sympathy, then their contempt when she rejects their gestures of kindness, doesn't know the language, and falls down into an epileptic fit. Indeed, her Indian name was ""Shivering Deer"" thanks to her grand mal epileptic seizures.

Mike takes her in, but the only members of the family she trusts and feels comfortable with, especially with her faltering English, are Sully, then Brian. Brian, however, becomes decidedly less enamored of her when he accidentally glimpses Catherine kissing Sully. Later, when Brian confronts Sully, he doesn't understand Sully's distinction between ""being kissed"" and ""kissing someone,"" and troubled, tells Mike about it.

Meanwhile, Jake, in a conversation with Loren and Dorothy about what marauding Indians do to white

Robert E buys a house in town. When the auctioneer, Jedediah Bancroft, sees that he's sold the house to a black man, he tries to renege, but Mike intercedes. Later, Mike is surprised to learn that Jake, Loren, Hank and Dorothy are displeased to have Robert E and Grace living in their midst.

That night, at the homestead, Matthew tells Mike he's been invited to join a new men's club -- the Ku Klux Klan, which he knows nothing about but is heading out the door to investigate. At the meeting, Jedediah, the leader of the group, promises only ""a big surprise"" for the following night, then adjourns the meeting. The next night, townsfolk don white gowns, recite the KKK oath, and ride out to harass and beat Robert E. After treating Robert E, Mike storms into the barbershop, where she confronts Jedediah, Jake, Loren and Hank about the events of the night before. Jedediah tries to make offers to get Robert E and Grace out of town, even threatening Mike with the mortgage on her clinic if Robert E

Rev. Johnson's in love with the town's new schoolteacher (Sherry Hursey), while Mike's concerned about the woman's wanton use of corporal punishment in the classroom.

Mike receives a telegram from Miss Olive - she's ill - but when she, family and friends arrive in Mexico, Miss Olive's already passed away and left 200 cattle to Matthew. Now they must get the herd back home. Colleen gets a crush on a handsome ne'er do well cowhand named Jesse, only to be robbed and deserted by him.

Matthew and Sully quarrel over the route of the cattle drive.

Mike and Sully battle money issues when Sully wants to be the primary provider and Mike wants to combine their incomes - in the end, it's Sully who comes around. Also, Myra becomes a sleepwalker, driving Horace crazy, but happily, the sleepwalking turns out merely to be a symptom of Myra's pregnancy.

Mike intervenes in their behalf when a Jewish peddler family arrives in town and is met with prejudice and harassment from townsfolk. Also, Matthew masquerades as Santa Claus for Brian. Guest star: Trisha Yearwood

Mike loses custody of Brian and Colleen when their father, Ethan Cooper, arrives with new bride Lillian and reclaims them in a messy courtroom battle. Also, Myra and Horace are almost driven out of their minds by new baby Samantha's incessant crying.

Brian and Colleen run away from Ethan and Lillian, and Colleen contracts potentially lethal pneumonia, which, upon the kids apprehension, Mike treats. Also, surprisingly, Hank's the only person who can quiet Samantha, Myra and Horace's eternally crying baby.

Dorothy Jennings' book about her experiences in Colorado Springs becomes a best seller, but it angers townsfolk.

Dr. Mike celebrates her birthday by climbing Pikes Peak with Dorothy, Grace and Myra, but ends up injured and alone when her companions turn back.

Dorothy, Myra and Grace realize they are quitting and they're letting Mike down, so they decide to go back. They find her injured with a broken arm. Mike can't go to the top of the mountain anymore, but she encourages the others to make it to the top for her. Meanwhile back in town, Preston plots to guild a hotel-casino with help from his ""partner"" Jake; and Robert E is bothered by an encounter with a bounty hunter.

Sully pursues a renegade mountain man who has kidnapped senator Leonard's son, in protest of the Senator's support of Colorado statehood. Meanwhile, Mike is forced to stop her practice when her schedule threatens her pregnancy. Ezra Leonard: Lawrence Pressman. Noah McBride: Denny Miller. Dr. Cassidy: Jerry Hardin.

The rescuers get ugly after Leonard offers a bounty for the mountain man, so Sully sets off alone.

Dr. Mike is arrested and put in jail for treating a fugitive Indian; Jake and Preston run against each other for mayor of Colorado Springs.

Grace and Robert E. encounter fierce opposition when they attempt to enroll their son in the town's all-white school.

Dr. Mike's Uncle Theodore, a concert pianist, sees in Brian not only a talented musician, but his own dead son.

When Colleen, who is working on a college paper, asks Dr. Mike to recall her most memorable case, Dr. Mike looks back on the five turbulent years she's lived and loved in Colorado Springs. As they sit with Andrew, who is mysteriously ill at the clinic, Dr. Mike reminisces about her tumultuous career -- its successes and its failures -- and realizes how many divergent cases she has seen and treated.

When Andrew's condition takes a turn for the worse, Dr. Mike warns Colleen about the fine line between emotional involvement and professional detachment, an issue with which she has long struggled in the frontier town that's now her home.